Response – problem solving to tackle knife crime

Knowing an intervention’s track record of successful or unsuccessful use is clearly important. Indeed, when embarking on any problem solving project, it is useful to find out what has been tried previously to address similar problems, and to what effect. Similarly, it is important to critically assess what has been done locally to address the problem, and ask why the problem remains.

But knowledge of an intervention’s track record takes us only so far. The challenge of crime prevention is that responses seldom work everywhere and every time. What worked to reduce knife crime in Liverpool may not work to reduce knife crime in London.

The problem may differ (for example, gang-related or robbery), the location may differ (for example, city centre or housing estate), the perpetrators and victims may differ (for example, similar or different demographics), and so on.

Local knife crime problem – will a response work for me?

The inconvenient truth of crime prevention is that you can never answer this question with a definitive ‘yes’. Crime is too complex to state with absolute confidence that a given response will work in every place and every time. Context matters. What you can do is gauge the plausibility of your selected responses and assess whether they make sense, based on what is known about your local problem. Because we cannot be sure that a given intervention will work, evaluation is therefore important. We return to this in the Assessment part of this guide.

Common responses to knife crime

Listed below are eight common responses to tackle knife crime, as identified from previous research and through consultation with police forces and Violence Reduction Units.

These responses fall into two broad categories.

Reducing the incidence of crimes involving knives

• school-based knife crime interventions
• police stop and search
• focused deterrence
• import enforcement

Reducing the likelihood that individuals will carry and/or use knives

• knife sweeps
• knife bins
• knife arches
• knife crime interventions based on ‘teachable’ or ‘reachable’ moments

In this section of the guide and for each of the eight responses listed above, we summarise what is known from the research evidence organised around the EMMIE evaluation framework. We present a logic model outlining how each response is expected to work, as well as ‘outputs’ and ‘outcomes’ (an important distinction) so that we might see if the response is working.

We also present potential negative side effects, which are highly important in the context of knife crime. Evidence shows that crime prevention activities can sometimes backfire and make matters worse (Welsh and Rocque, 2014); (Braga, 2016). This may occur because of the content of an intervention (that is, what people are asked to do) or because of the way in which it is delivered. In relation to the latter, much research shows that police interventions that are experienced as ‘procedurally fair’ (that is, respectful, inclusive, neutral and unbiased) tend to be viewed by the public as more legitimate, are more likely to garner greater cooperation and are therefore more likely to generate the desired crime-reduction goals (Bolger and Walters, 2019).

Many of the knife crime responses presented here require community support and involvement. The potential for unintended community harm is therefore ever-present. Being open to, and mindful of, the possibility of unwanted side effects is important when problem solving. This will allow you to identify the early signs of possible backfire effects and, where necessary, take corrective action.

Before proceeding, some qualifications are needed. First, although the responses included here are presented separately, efforts to reduce knife crime often involve a combination of different responses, sometimes implemented sequentially (such as enforcement efforts targeted at prolific offenders followed by community-oriented interventions).

Second, the menu of responses presented here is not an exhaustive list of all the tactics that might be deployed to tackle knife crime. Responses discussed here are those that were most frequently identified by interviewees and focus group participants consulted as part of this research. You may find other relevant interventions in the Crime Reduction Toolkit.

Third, the responses and logic models presented here are meant to inform, not dictate, how you deal with your local knife crime problem. Not all responses will be suitable for all circumstances. Nor should you limit yourself to approaches that have been tried before. Problem solving is a creative endeavour – innovation is encouraged.

Fourth, despite the scale and harms of knife crime, the evidence base for knife crime reduction is underdeveloped. Robust evaluations of the impact of common knife crime interventions are sparse (McNeill and Wheller, 2019)..

What is the focus of the school-based interventions?

There is a wide array of schools policing programmes, including primary interventions (such as education and awareness-raising) and secondary interventions (such as the identification and referral of pupils deemed to be at risk of involvement in knife crime, intelligence gathering and situational prevention of knife crime in, and around, schools). Note that ‘primary’ and ‘secondary’ refer here to types of intervention, rather than school types.

Effect – have school-based interventions been shown to reduce knife crime?

Evidence on the impact of schools policing programmes is mixed and sparse (Posch and Jackson, 2021); (Raymond, 2010). Some studies have shown that locating police officers in schools on a full- or part-time basis is associated with positive outcomes, including reductions in truancy, reductions in involvement in crime, improvements in police-student relations and increases in students’ feelings of safety. Other studies find no clear effect of the presence of police in schools on levels of crime.

Although school-based interventions on knife crime often report a large number of outputs, such as the number of children engaged, evidence on the effectiveness of primary-type interventions in reducing violence is lacking, in part because involvement of school-age children in knife crime is rare (Ramshaw, Charleton and Dawson, 2018).

Concerns have been raised about potential unintended negative consequences associated with greater police presence in schools, including the increased criminalisation of children (‘net-widening’), stigmatising of children and areas receiving police in schools and breeding hostility between students, parents and the police.

Mechanism – how do school-based interventions work?

Schools policing programmes can target knife crime through primary interventions that are relatively untargeted, such as:

• raising students’ awareness about the risks and consequences of routine knife carrying
• developing students’ abilities to resist pressure to carry knives
• challenging, and ideally changing, (perceived) social norms about knife carrying and knife crime
• building stronger bonds with, and trust between, the police and students

More targeted secondary and tertiary interventions are also available tactics, such as:

• referring children found to be at risk of knife crime to allied services and support options
• the gathering of intelligence relevant to knife crime

In addition, the presence of police may also reduce incidents of knife crime within the school itself, through increasing the perceived risks associated with being caught carrying a knife.

Moderator – In what contexts do school-based interventions work best?

Schools policing programmes are likely to be more effective when:

• carried out in collaboration with the affected schools and partners
• targeted at pupils liable to carry knives
• delivered in a manner that is perceived to be (and experienced as) just, appropriate and respectful, in accordance with the principles of procedural justice

There are also ethical concerns about what (level of) intervention is appropriate in educational settings. It is therefore essential that school-based policing activities are appropriate for the age of the child or group. Useful guidance can be found in ‘Police in the classroom: A handbook for police and PSHE teachers’ (PSHE Association and NPCC, 2019).

Implementation – what is known about implementing school-based interventions?

Noted barriers to successful implementation include inadequate contact between police officers and school children, bottlenecks in referrals to allied services, minimal buy-in from school children and challenges in retaining staff to consistently deliver school-based interventions over the long term (as opposed to one-off bursts of activity).

Economics – what is known about the costs and returns of school-based interventions?

Both schools and police services clearly incur costs in developing local material and delivering school-based interventions focused specifically on knife crime, which need to be warranted in light of other diverse demands on both school and police resources.

General considerations

It is unlikely that primary interventions like school-based information sessions on knife crime are harmful and their cost is low. However, the rare nature of knife carrying and involvement in serious violence means that, for a large proportion of young people, lessons around knife crime may not be directly relevant. With regard to secondary and tertiary interventions that target specific groups within a school, it is essential that age factors and the ethical appropriateness of these activities are considered. There is the potential for backfire effects, such as damaging trust in the police and stigmatisation of young people.

What is the focus of the stop and search intervention?

Stop and search is a collection of legal powers, derived from section 23 of the Misuse of Drugs Act 1971 and section 1 of the Police and Criminal Evidence Act 1984, which allow police officers to search people whom they have grounds to reasonably suspect to be in possession of prohibited items (such as weapons or drugs) or stolen goods. Section 60 of the Criminal Justice and Public Order Act 1994 allows searches to be carried out without suspicion in a defined area for a fixed period of time (usually 24 hours) when authorised by an officer of rank inspector or above.

Effect – Has stop and search been shown to reduce knife crime?

Evidence on the effectiveness of police stop and search to prevent crime is modest. A study conducted by the College of Policing indicated that changes in the rate of police stop and searches in London were not associated with any discernible changes in crime (Quinton P, Tiratelli and Bradford, 2017). Evidence regarding the use of stop and search as part of ‘hotspot’ policing or as part of an everyday level of police activities strategies is more favourable. However, the precise role that stop and search plays within hotspot policing is less clear (Braga, Papachristos and Hureau, 2012); (Ratcliffe and others, 2011); (Weisburd and others, 2015); (Del Toro and others, 2019).

Concerns have also been raised about ethnic disproportionality in police use of stop and search. Where the use of stop and search is perceived to be unfair or disrespectful, it can have damaging consequences. These may include lower levels of trust in the police, reduced legitimacy of the police, people being less willing to cooperate with the police and even people being more willing to break the law (Del Toro and others, 2019).

Mechanism – How does stop and search work?

The legal purpose of most stop and search powers are to support a police officer, where they have reasonable grounds, by enabling them to search for prohibited articles. By extension, this enhanced potential to detect crime may have a deterrent effect that is expected to reduce (knife) crime in the local vicinity.

Use of stop and search may increase the risk, perceived or actual, that those in possession of or using a knife will be apprehended.

This deterrence effect may operate at two levels:

• knowledge that the police have the power to perform stop and searches may deter those liable to carry knives (general deterrence)
• experience of being stopped and searched may make an individual perceive knife possession as being too risky and they may therefore no longer carry a knife (specific deterrence)

The recovery of knives seized through stop and search may also reduce knife crime through decreasing the stock and/or availability of knives for criminal purposes.

Finally, intelligence generated through stop and search interactions may assist crime reduction.

Moderator – in what contexts does stop and search work best?

It is likely that stop and search works best in investigating and deterring crime when it is deployed cautiously and sensitively through the use of supporting intelligence and when accompanied by other interventions.

The potential backfire effects of stop and search are likely to be reduced when:

• there is a genuine and objectively reasonable suspicion that a person is in possession of a prohibited article or item for use in crime
• individuals are informed and understand why they have been stopped and searched, and are treated justly and respectfully
• affected communities understand why stop and search is being used and are able to give feedback to the police about their perceptions and experiences

Implementation – what is known about implementing stop and search?

It is important that the targeting of places and persons – as well as its manner of use – is lawful, necessary, proportionate, and procedurally and distributively fair. This is the case in the interests of maximising effectiveness, maintaining public confidence and police legitimacy, and maintaining adherence to the key principles of British policing.

Because of controversies over its use and concerns about the potential negative effects of stop and search, community consultation should be considered where possible in advance of its use in knife crime hotspots. Where this is not possible, an explanation should be provided once it has been initiated (College of Policing, 2015). Those involved in stop and search should be mindful of the principles of procedural justice and the potential for negative consequences if misused.

Economics – what is known about the costs and returns of stop and search?

Stop and search may be resource-intensive and hence expensive (Quinton, Tiratelli and Bradford, 2017). When used more frequently without strong justification and supporting intelligence, it is likely to yield diminishing returns. Stop and search needs to be used with caution, as the impact on community relations can be high.

What is the focus of the intervention?

Focused deterrence interventions (Scott, 2017) – also known as ‘pulling levers’ approaches – focus on offenders and members of groups and gangs, in this case making use of knives in crime.

Individuals and groups are called in collectively to meetings with the police. They are then informed that their identities are known and that if they persist in the specified criminal behaviours, the police have a wide range of enforcement options at their disposal. If knives continue to be used, enforcement action will be taken immediately and will apply to the individuals involved and the criminal peer groups to which they belong.

Close family and community members are also called in to meetings with known offenders and offender groups to voice their concerns about and disapproval of knife crime. In this approach, other agencies are also drawn in to engage with individuals to offer alternative life choices providing routes out of violent, criminal lifestyles.

Effect – has focused deterrence been shown to reduce knife crime?

There is evidence that focused deterrence strategies are associated with reductions in violence. However, this evidence comes overwhelmingly from studies undertaken in the US, which have focused on gun rather than knife crime (Braga and Kennedy, 2021). This type of intervention was found to be at its most effective when the unit of intervention was a group as opposed to an individual.

The positive effects of focused deterrence are also often found to extend beyond the targeted area or group, a phenomenon known as diffusion of crime control benefits. An evaluation of a focused deterrence programme in Scotland found promising reductions in the number of weapon-related offences in an intervention group compared to a selected control group (Williams and others, 2014). 

An evaluation of the US group violence initiative, Operation Ceasefire, in London in 2014-16 was inconclusive and suffered from severe implementation problems (Davies, Grossmith and Dawson, 2016).

Mechanism – how does focused deterrence work?

Focused deterrence can reduce knife crime in several ways, through:

• deterrence, by increasing the perceived risks and reducing the perceived rewards of knife carrying and use 
• focused informal social control (clear disapproval or shaming), applied by close kin and community leaders to those involved in knife crime
• informal social control applied within offending groups to avoid the broad-based enforcement attention that would follow if any group or gang member engaged in knife crime
• arrest of those individuals who persist in criminal behaviour
• the diversion away from knife crime, especially where gangs are involved, and towards alternative (non-violent and non-criminal) pathways

Moderator – in what contexts does focused deterrence work best?

Although focused deterrence can be used with individuals or drug markets, the impact of focused deterrence strategies is greatest when targeted at criminally active groups (Barthe, 2006). Focused deterrence can also only be applied where there is very strong intelligence on the individuals and groups involved in knife crime. This needs to be mapped carefully prior to the implementation of the intervention if it is to have good prospects of success.

Strong support from the affected communities and a willingness to collectively say ‘no’ to violence is also vital.

Finally, focused deterrence is both stick and carrot, offering either engagement or enforcement. The carrot relates to the offer of engagement with support services towards non-criminal pathways. It follows that the availability and speed with which support services can be mobilised is also an important determinant of success. 

Implementation – what is known about implementing focused deterrence?

The track record of implementation in the UK is mixed. Key elements of the intervention are sometimes omitted, meaning that the intervention is used selectively by those favouring only particular elements of it, instead of as a single coherent package. Focused deterrence requires skilled and informed implementation, as well as dedicated resources – for example, to fund diversionary opportunities.

Crude and poorly targeted measures would likely backfire by producing community resentment and mistrust of the police.

Economics – what is known about the costs and returns of focused deterrence?

Focused deterrence initiatives mainly require system changes leading to a focus on groups and individuals driving knife crime, rather than additional net resources, although effecting these changes may entail short-term costs as the changes are implemented.

Where key components cannot be provided by refocusing existing services, there may also be some additional longer-term costs, but these will vary by area. Where lives are saved or serious injuries are prevented, monetary costs can be quickly outweighed by monetised benefits.

General considerations

To date, the majority of focused deterrence studies have taken place in the US. Applications in the UK have not always been successful, although this is likely due to poor implementation.

What is the focus of import enforcement?

This intervention is a collaboration between the police service and Border Force. The Border Force identifies incoming packages suspected to be containing knives, with a particular concern for knives that are banned. They confiscate banned knives and destroy them. They pass on information about the destinations for knife packages intercepted to local police services.

Local police services follow up the information with consignees, to issue warnings (for instance, about sales to underage customers) or take other enforcement action as relevant.

Effect – has import enforcement been shown to reduce knife crime?

There are no published studies on the effectiveness of border force operations to reduce knife crime. The outcome effectiveness of this approach is therefore unclear.

However, anecdotal evidence suggests that such operations are effective in stemming the supply of some illicit weapons. Moreover, police follow-ups with sources and intermediaries – for example, websites through which knives are sold – have apparently led to reductions in the ease with which knives liable to be used in crime can be acquired.

It is not known whether thwarted offenders adapt by acquiring knives from different sources, or whether they simply give up efforts to acquire them.

Mechanism – how does import enforcement work?

Import enforcement operations can reduce knife crime in two main ways, through:

• making it more difficult to acquire knives for criminal use
• alerting suppliers to their civic responsibility or deterring them from the reputational risk they face if they are seen to facilitate the acquisition of knives for criminal purposes

Intercepted packages might also help identify individuals involved in the supply or usage of knives hitherto unknown to the police.

Moderator – in what contexts does import enforcement work best?

Import enforcement operations are likely to be more effective where there are efficient (prompt and reliable) communication channels between Border Force and local police services, and where follow-up visits by local police services are speedy and locally sensitive.

Efforts to change the practices of retailers found routinely to be supplying intercepted knives may require the support of senior officers and/or police and crime commissioners (or their equivalents).

Implementation – what is known about implementing import enforcement?

It can be difficult to distinguish suspicious and unsuspicious packages and/or destinations.

Moreover, the number of consignments potentially containing knives can be large, making the process of feeding back to – and following up by – local police services unwieldy. This has led to more focused or targeted follow-ups.

Economics – what is known about the costs and returns of import enforcement?

There is a significant investment associated with both Border Force identifying packages and liaising with local police services, and from local police services and their partners (for example, Trading Standards) following up on the intelligence received.

General considerations

Border Force collaborations with police have the potential to lead police to the homes of people involved in a range of crimes. Alternatively, they may also reveal the addresses of vulnerable individuals who have been coerced into using their address for delivery of weapons, thus identifying exploited victims.

Consideration should be given to this possibility when following up on import enforcement intelligence.

What is the focus of knife sweeps?

Police searches of locations where knives are believed to have been discarded or hidden for later use. Knife sweeps are sometimes undertaken in collaboration with the community. The knives recovered during sweeps are often publicised through print and social media. Acquired weapons are then destroyed. Sweeps may be used in different ways – for example, as weeks of action in knife crime hotspots, or in response to specific intelligence.

Effect – have knife sweeps been shown to reduce knife crime?

There is evidence to show that knife sweeps result in the identification of knives and can be positively received by the community (an output). There is limited evidence to show that knife sweeps are associated with reductions in knife crime and associated harms (outcomes).

Indirectly related to knife sweeps is evidence that clearing overgrown areas is associated with a reduction in firearm violence (Branas and others, 2018). In this and similar studies, researchers have suggested that clearing these areas reduces the number of places that a gun can be hidden in a community, thus reducing firearm accessibility when the opportunity for violence arises and reducing opportunities for disposal once a weapon has been used. While this mechanism matches that of knife sweeps, an alternative explanation is that clearing overgrown areas are effective because they limit opportunity for criminal association or the act of clearing may increase natural surveillance in the area. Therefore, the success of clearing overgrown areas cannot confidently be generalised to knife sweeps.

Mechanism – How do knife sweeps work?

Knife sweeps may reduce knife crime in three main ways:

• the accessibility of knives secreted in locations where they can be accessed for criminal purposes
• the stock or circulation of knives that can be used in crime
• the perceived need to carry knives for defensive purposes, if it is believed that others will be denied access to knives

Insofar as knife sweeps are effective, those effects may be extended if those liable to carry knives over- or under-estimate the operational range and timeframe of knife sweeps. Knife sweeps may also help with community engagement where visible action is taken against knife crime.

In terms of backfire effects, it is possible that advertised knife sweeps may give rise to offender adaptation, whereby offenders opt to use other weapons and/or knives are secreted in different locations and at different times not covered by the knife sweeps. It is also possible that publicising the types of knives found in a given area might increase fear of knife crime among some individuals, thereby increasing knife carrying for defensive purposes.

Moderator – In what contexts do knife sweeps work best?

Knife sweeps are likely to be more effective if reliable intelligence indicates that knives used for criminal purposes are secreted for future offensive or defensive use, and identifies the locations where such knives are likely to be hidden and/or discarded.

Implementation – What is known about implementing knife sweeps?

Deficiencies in intelligence and/or analysis about where knives are routinely discarded may make the targeting of knife sweeps more imprecise. Limited availability of personnel to conduct sweeps will clearly restrict the impact of this intervention.

Economics – What is known about the costs and returns of knife sweeps?

Knife sweeps are relatively low-cost. Much of the cost associated with knife sweeps relates to the analysis necessary to identify suitable locations and the deployment of police officers (and other partners and volunteers) who are searching for knives. However, as with all interventions, there are opportunity costs, whereby those resources devoted to knife sweeps could be put to alternative uses.

General considerations

The knives seized during knife sweeps may not be representative of the types of knives used for criminal purposes in your area. To explore this, it may be helpful to compare the proportion of different knife types acquired through knife sweeps to the proportion of knives used in crime (as measured by police-recorded crime data) and seized via stop and search.

What is the focus of the knife bin intervention?

A purpose-built secure unit where knives and other sharp objects can be disposed of safely and anonymously.

Effect – Have knife bins been shown to reduce knife crime?

There is evidence to show that when knife bins are placed in a community, they are used (an output). However, it is unclear if the types of knives deposited in bins match the types of knives used in the commission of knife crimes. There is also limited evidence to show that the use of knife bins is associated with reductions in knife crime (outcomes).

Little rigorous evaluation of knife bins or knife amnesties has been undertaken. There is some evidence that knife-related offences decreased in the months following a national knife amnesty (the Tackling Knives Action Programme) in 2006, wherein 90,000 knives were collected over a six-week period (Metropolitan Police Service, 2006). However, the study design, which compared rates of knife violence in short periods before and after the knife amnesty, and which did not include a comparison area, limits the extent to which the observed decrease in knife crime can be attributed to the knife amnesty.

In related research, gun buyback schemes, which aim to reduce the number of available firearms in a community by exchanging firearms for money or gift tokens have been evaluated in Australia and the US. These interventions have been found to have little direct effect on firearm-related violence (Makarios and Pratt, 2012). Furthermore, analysis of the types of guns surrendered through gun buyback schemes and amnesties found that they were not the types of guns commonly used in gun violence (Kuhn and others, 2002).

Mechanism – how do knife bin interventions work?

Knife bins may reduce knife crime in two main ways, by reducing:

• the stock or circulation of knives that can be used in crime
• the perceived need to carry knives for defensive purposes

Knife bins may also help with community engagement through being seen to take action against knife crime, particularly if paired with local media coverage and appeals to the public to share information pertaining to knife crime. While sometimes coordinated by police forces, bins may also be operated by community groups in ways that facilitate the anonymous disposal of knives.

There are several potential backfire effects associated with knife bins. The presence of knife bins may provide cover for individuals found carrying knives locally – for example, ‘I was just taking my knife to put it in the knife bin’. It is possible that the placement of bins in certain neighbourhoods may increase the fear of knife crime and the perceived need among some individuals to carry knives for defensive purposes.

Knife bins may also stigmatise neighbourhoods in which they are located as dangerous high-crime areas. Finally, knife bins may give rise to defiant acts – for example, through attempts to break into them, deposit needles or paint graffiti on them. These acts of defiance, if left unchecked, may undermine the police image in the affected neighbourhood.

Moderator – In what contexts do knife bins work best?

Knife bins are likely to be more effective if placed in locations where intelligence indicates that knife crime is more prevalent and where there is a reluctance or limited opportunity to dispose of knives safely and securely.

Implementation – What is known about implementing knife bin interventions?

The potential impact of knife bins may be undermined if the bin is damaged or defaced. A quick response to address these issues is important. There is anecdotal evidence about the difficulties experienced in mobilising third parties to routinely empty knife bins.

Economics – What is known about the costs and returns of knife bins?

There is an initial outlay associated with the purchase of knife bins but once purchased, the bins are relatively low-maintenance and there are limited associated personnel costs.

General considerations

There is noted variation across forces in where knife bins are located. Some opt for locations near police stations. Others elect to install bins in locations where knife crime activity is known to occur. Others opt for ‘neutral’ locations, such as churches.

Like knife sweeps, the knives deposited in knife bins may not be representative of the types of knives used for criminal purposes. This again can be explored by comparing the proportion of different knife types acquired through the deployment of knife bins to the proportion of knives used in crime (as measured by police-recorded crime data) and seized via stop and search.

What is the focus of knife arch interventions?

A walk-through metal detector to identify the presence of knives and other metallic offensive weapons. Knife arches are often accompanied by both uniformed and plain-clothed police officers, in part to identify, engage with and, where grounds exist, search those individuals who actively avoid walking through the detector.

Effect – have knife arches been shown to reduce knife crime?

There is evidence to show that knife arches result in the arrest of individuals carrying knives and the confiscation of their weapon (an output). They are also widely credited with preventing knives and other metallic offensive weapons from entering specific locations covered by knife arches, such as selected schools, sporting events and festivals.

However, there is limited evidence to show that the use of knife arches is associated with reductions in knife crime and associated harms (outcomes). Evaluations of the use of metal detectors in US schools65 and hospitals66 indicate that they have limited impact on violence rates but may reduce overall severity of violent injury. Evaluations that have sought to test the impact of metal detectors on feelings of public safety have been equivocal. Some have found that they improve it, while others have concluded that they damage it.

Mechanism – how do knife arches work in reducing knife crime?

Knife arches may reduce knife crime in two main ways:

• by increasing the perceived likelihood of being caught in possession of a knife
• by reducing the accessibility of knives for criminal use through confiscating those detected by the arch

In a general sense, knife arches may help with community engagement through the police being seen to take action against knife crime. More specifically, knife arches might improve feelings of safety where they are used as a condition of entry at certain locations (such as sporting events and festivals). Knife arches also provide an opportunity for police officers to engage positively with members of the public passing through the knife arch.

Knife arches may also reduce other forms of crime. For example, those in possession of drugs might actively avoid the knife arch, thereby providing grounds to be stopped and searched by the police.

In terms of backfire effects, the use of knife arches may result in more offenders hiding knives in certain locations in an effort to avoid knife arches.

Moderator – in what contexts do knife arches work best?

Knife arches are likely to be more effective when deployed strategically in locations where intelligence indicates there is a high volume of knives passing through and/or where the presence of knives might provoke violence. Key to the effectiveness of knife arches is the use of officers to detect those who double back to actively avoid passing through the arch. For this reason, having a sufficient number of strategically placed police personnel is an important part of this response.

Implementation – what is known about implementing knife arches?

The deployment of knife arches can be time-consuming. Moreover, knife arches may place a burden on the general public, leading to delays in movement and hence public resentment. This can be a significant challenge when deployed in areas with high footfall (such as busy train stations).

Economics – what is known about the costs and returns of knife arches?

Knife arch operations can be expensive. There is a significant cost associated with purchasing and maintaining the knife arches. Knife arches also need to be ‘worked’ and so the cost of personnel (both uniformed and plain clothes) must also be factored in.

General considerations

Knife arches involve members of the public coming into contact with the police. Overwhelmingly, these individuals will have nothing to do with crime in general or knife crime in particular. Consequently, it is vital that the interactions with the police are experienced as procedurally fair, whereby the police inform affected individuals of the rationale for the knife arches and, where appropriate, why they are being stopped and searched. This is especially important for knife arches because, in public places, members of the public are not legally obliged to walk through the knife arch.

Insofar as knife arches are effective, evidence is currently unavailable as to the relative contribution of the two dominant mechanisms accounting for those effects – increased risk of detection or increased seizure of knives. If it is the former, and in light of the high costs of knife arches, one consideration is whether the same risk-increase mechanism could be activated in cheaper ways, such as through the use of high-visibility police officers.

What is the focus of the teachable moments intervention?

A ‘teachable moment’ is an unplanned opportunity or event where the likelihood of changing someone’s behaviour is maximised. Recognising and taking advantage of teachable moments now forms the basis of many behavioural change programmes in education, health and policing, usually directed at young people.

Attendance in hospital or a trauma centre as the result of a violent injury is widely considered to be an example of a teachable moment, as is detention in police custody following arrest. The potential for intervening at teachable moments has given rise to a series of interventions involving structured interactions, typically between the affected young person and the police, youth workers and/or relevant hospital staff.

These interactions, which can vary widely from mentoring to life skills coaching, are designed to:

• encourage the young person to reflect on their current circumstances
• offer him or her longer-term support – a ‘wrap around’ service – attending to their particular social needs and designed to initiate a positive change in their behaviour

Effect – Has it been shown to reduce knife crime?

There is little high-quality evidence to show that UK-based hospital-based interventions targeted at young people during ‘teachable moments’ are effective in reducing criminal involvement and repeat hospital attendance. Some evaluations have reported positive outputs in the form of contacts with eligible clients (Goodall, Jameson and Lowe, 2020), but there is limited evidence to date that these interventions are associated with reductions in violence or weapon-related offences.

Similar hospital-based schemes have been evaluated in the US and returned similar results.

Although some positive results were obtained in terms of contacts and reductions in self-reported injury, this small number of studies experienced issues with high and biased intervention drop-out and difficulties in obtaining follow-up data (Chong and others, 2015).

Evidence of the effectiveness of custody-based interventions is mixed, in part because of the varying nature of interventions that begin in custody and that seek to capitalise on a ‘teachable moment’. Some are implemented as a combination of diversion from punishment and teachable moment (‘pre-charge’), while others simply apply the principles of teachable moments after criminal processing (‘postcharge’).

In the former, more serious violent and weapon-related offences are often ineligible for pre-charge diversion programmes, so the evidence that they are effective – at least with young people – in reducing re-arrest (Wilson, Brennan and Olaghere, 2018). cannot be generalised to most violent offending. Post-charge interventions are growing in popularity in the UK and elsewhere but there has been little rigorous evaluation of their effectiveness in reducing violent re-offending (Lynch-Huggins and others, 2021).

Mechanism – How do teachable moments work?

Teachable moments programmes can reduce knife crime in several ways:

• through encouraging the victim in hospital or the arrestee in custody to consider and question the seriousness of their current circumstances and recognise their own vulnerability 
• through treating hospital attendance or arrest as possible ‘turning points’ where a change in lifestyle is possible
• by setting out and offering assistance in taking advantage of alternative, pro-social life choices

In terms of backfire effects, it is possible that hospital-based teachable moments programmes might inadvertently increase a person’s sense of vulnerability and increase their likelihood of weapon carrying, or that custody-based teachable moments might reinforce the arrestee’s criminal identity. They may also risk alienating recipients if victims of knife crime consider themselves to be labelled as knife crime perpetrators.

Moderator – In what contexts do teachable moments work best?

Hospital-based teachable moments programmes are likely to be more effective in reducing knife crime in areas where there is a high degree of victim-offender overlap, where there are strong police–healthcare–youth worker partnerships able to quickly attend hospital in the immediate aftermath of a knife injury, and where follow-up services are available, suitable and sufficiently funded. Evidence also suggests that impact can be maximised when using trained professionals to deliver interventions at teachable moments. Implementation – What is known about implementing the intervention? Noted barriers to implementation include failure to recruit, train and retain the staff needed to deliver the intervention and bottlenecks in referring participants to relevant allied services, which then limits the longer-term potential impact from intervening at the teachable moment.

Economics – What is known about the costs and returns of the intervention?

There are substantial potential cost savings associated with reductions in criminal involvement, hospital attendances and the harms caused by related risky behaviours. However, teachable moments programmes are also resource-intensive and therefore may be more cost-effective in settings where there are a lot of knife injuries or arrests related to knife crime. There are significant costs associated with the hiring, training and funding of staff tasked with delivering these interventions. There are also costs associated with running the longer-term support services typically offered as part of this response.

General considerations

Participation in this type of programme is voluntary. Previous studies report both low initial take-up rates and high attrition over the course of the intervention. These observations limit the confidence with which findings can be generalised. It should also be acknowledged that in certain circumstances, the term ‘teachable moment’ is considered inaccurate, and ‘reachable moment’ might be more applicable.

The latter is generally used when referring to individuals who may be exploited or in vulnerable circumstances, and may not have the choice to change the direction of their lives (because they are under duress, offending for sustenance, addicted to drugs, and so on), or cannot be ‘taught’ (they perhaps already know), but rather they need ‘reaching’ and taking out of the circumstances they are in.