Stop and search and knife crime in London: what we know and what we don”t

Blog post

Stop and search and knife crime in London: what we know and what we don”t

There have been increasing concerns in recent months about signs of a rise in knife crime in London, particularly involving young people. After a period of sustained falls in the use of stop and search by the Metropolitan Police, some commentators including the Metropolitan Police themselves have suggested that the rise in knife crime may partly be related to the reduction in the use of stop and search. This blog sets out the recent arguments and clarifies what we do and do not know.

The recent debate about stop and search in London

In September, two MPS Commanders gave an interview to the Guardian newspaper, in which they are reported to have said four factors were behind’ an 18 per cent rise in knife crime:

– Reductions in the use of stop and search.

– Improved recording of knife crime statistics.

– The dark web’ being used to purchase exotic weapons.

– A cultural change’ among young people that is encouraging’ them to use knives.

In September at the GLA Police and Crime Committee, Commissioner Bernard Hogan-Howe claimed that “over the last three years [as stop and search use has fallen] we arrested more people and violence came down, stabbings came down” and suggested that there “is some evidence that [this trend] has bottomed out”. So he effectively asserted that police activity had resulted in a reduction in stabbings. He went on, “[f]or the last three months we have said we are going to increase [stop and search] in a targeted way We are increasing it in a reasonable way in those areas where we think it needs to happen”. He described as a possibility’ the assertion that a reduction in stop and search might embolden’ some people to carry knives, but was not more definitive than that.

Yesterday the Home Secretary gave a speech in which she stated, “arrest rates are rising. Police time is being saved. Trust is being rebuilt. We must not jettison all that good work for the sake of a knee-jerk reaction on the back of a false link.” Her speech highlighted that four-fifths of the fall in stop and searches in London is accounted for by falls in stops and searches for drugs and stolen property, in relation to which she said “it is simply not true that knife crime is rising because the police are no longer stopping and searching those carrying knives”. That infers that stop and search for reasons other than weapons possession does not deter weapon carrying.

The Metropolitan Police responded with a statement that included the following:

Our clear intention is to continue with the targeted use of stop and search, and the Home Office appears to have misunderstood our response to recent rises in knife crime and our future intentions. There has been no knee-jerk reaction nor will there be.

What there has been is a disturbing increase in the number of murders and stabbings, often with young black men the victims. It was only right that the MPS acknowledged what has been suggested anecdotally – that the reduction in stop and search may have reduced the deterrent to carrying knives.

However, whilst the Commissioner has acknowledged this is a possibility, he made it clear that there is no definitive evidence to prove or disprove the suggested link. That remains our position.

We will do all we can to reduce knife crime, to tackle London’s gangs and take more knives and weapons off our streets.

Stop and search is one of many tactics we will use, and it can remove knives from our streets and deters youngsters from carrying them.

At issue then is:

  • Whether knife crime is increasing.
  • Whether stop and search and knife crime are related, and if so the nature of that relationship in particular whether it is causal.
  • Whether an increase in stop and search is an appropriate response to any increase in knife crime.

What we do know:

  • Figure 1 below shows stop and search and knife crime with injury in the MPS between 2008 and 2015.
  • No-one has suggested that the police should not have stop and search powers.
  • Stop and search in London has fallen by around three-quarters since 2011, from a peak of around 50,000 per month to a low of around 12,000 (see notes below for definitions).
  • More than half of that fall predates the Home Secretary’s reforms of stop and search, which were announced in April 2014.
  • The proportion of stop and searches that result in an arrest rose from around 7 or 8 per cent in 2008-11 to around 20 per cent in mid-2015, suggesting that stop and search has become increasingly targeted.
  • In 2014/15 there were 180,460 stops and searches and 1,342 knife possession offences recorded by the Metropolitan Police (not all of the knife possession offences will have resulted from a stop and search).
  • Between 2012/13 and 2014/15 the number of stops and searches halved, while the number of knife possession offences fell only 4 per cent.
  • Knife crime and serious youth violence’ fell sharply between 2011 and 2012 and remain below the levels seen from 2008 to 2011, but have begun to increase.
  • Knife crime is highly seasonal, being higher in the summer months and lower in the winter; trends can only be discerned by looking at longer-term data (at least one year).
  • Most of the fall in stop and search happened before knife crime began to increase.
  • Stop and search can result in useful intelligence even when it does not result in arrests.
  • Following criticism and scrutiny, changes to crime recording practices have resulted in artificial increases to police recorded crime rates across England and Wales, particularly for less serious forms of violence.
  • London Ambulance Service knife injury’ data shows similar patterns to Metropolitan Police knife crime with injury’ data, including a very slight increase in recent months, suggesting that there has been a genuine increase in knife crime.
  • Levels of knife injury remain well below those seen in 2010 and 2011, before the fall in stop and search.
  • Levels of knife crime and violence are likely to be the result of multiple factors of which police activity (including stop and search) may be one.

There are some consistencies in knife crime trends in recent years when comparing the MPS to the West Midlands, Greater Manchester and West Yorkshire. This suggests that rises in knife crime in London may partly be caused by wider factors that are not specific to London.

What we don’t know:

  • There is no evidence that reductions in stop and search have caused knife crime to increase.
  • There is some research evidence from the US that stop and search has a deterrent effect compared to no stop and search at all, but no empirical evidence about the marginal effect of stop and search on deterrence (in other words, how much deterrence you get for x additional stop and searches).
  • We don’t know the degree to which changes to police crime recording practices have impacted on published knife crime data, although any impact is likely to be greater for less serious types of offences.
  • There are signs in the data that falls in knife crime and youth violence followed the riots in August 2011, but it is not clear if there is a causal relationship (for example, because of arrests, imprisonment and other deterrent effects).
  • We don’t know the extent to which cuts to police and wider public service funding are reducing efforts to prevent young people engaging in violence.
  • We don’t have any firm evidence about the significance of exotic knives purchased on the so-called dark web’, or the use of these instead of or in preference to more mundane weapons.
  • We don’t have any firm evidence about changing cultural attitudes among young people to violence and weapons.
  • We don’t at this stage know if there have been any changes to data recording practices by the London Ambulance Service.

Next steps:

The Police Foundation is currently talking to the MPS and other large forces to access additional data for analysis. We intend to publish a briefing presenting this analysis in more detail in due course.


The Police Foundation has published a range of charts on Twitter examining stop and search and knife crime in London: (and Gavin Hales’s replies).

Stop and search and crime data for the Metropolitan Police are available from the London Datastore

The definition of stop and search used in these data is: Total number of Stops and Searches under PACE (Police and Criminal Evidence Act), S23 Drugs Act, S47 Firearms Act plus a very small number not included in the other categories (e.g. s163 Road Traffic Act). This excludes stops and searches conducted under s60 Criminal Justice and Public Order Act (generally referred to as section 60′ stops and searches).

London Ambulance Service data are also available from the London Datastore:

Figure 1: stop and search and knife crime with injury in the MPS


View larger image here