The use of large “surge” stop-and-search operations by the police has no discernible effect in reducing crime, according to newly released Home Office research.

The study looks at the mass use of stop and search by London’s Metropolitan police to tackle knife crime in 2008/09, at a time when officers were carrying out one search every 20 seconds on average nationwide.

The study was released following a Freedom of Information request by the Guardian and its findings directly impact on the recent debate between the home secretary and the Met commissioner over whether a rise in knife crime can be linked to falls in stop and search.

The use of large-scale mass stop and search operations has been highly controversial not least because black people are still four times more likely to be stopped and searched on the streets by the police than white people.

The home secretary, Theresa May, launched a major campaign to scale back the mass use of stop and search by the police and to replace it with targeted operations on crime hotspots designed to improve arrest rates. She has argued large-scale stop and search operations can poison community relations.

The official evaluation looked at 10 London boroughs which saw a threefold increase in weapon searches by the police, up from 34,154 in the year before to 123,335 in the first year of Operation Blunt 2, which began in the spring of 2008.

It also compared crime rates in a further 16 London boroughs, which saw a much smaller increase – up 18,103 – in weapon searches over the same period.

The researchers looked at nine different measures of police recorded crime including assaults involving a knife, robbery, and weapons and drug possession offences.

But their analysis found “no statistically significant crime-reducing effect from the large increase in weapon searches during the course of Operation Blunt 2. This suggests that the greater use of weapons searches was not effective at the borough level for reducing crime.”

The Home Office researchers say their analysis was confirmed by data from the London Ambulance Service showing that callouts for weapons injuries did not drop more in the boroughs targeted for the mass use of stop and search than the other boroughs: “Rather, ambulance callouts actually fell faster in those boroughs that had smaller increases in weapons searches.”

They add that both types of boroughs saw reductions in the number of murders involving stabbings during the period but say the small numbers involved mean that it is unlikely the falls in the mass stop and search boroughs could be attributed to the police operations.

“Overall, analysis shows that there was no discernible crime-reducing effects from a large surge in stop and search activity at the borough level during the operation. However, it does not necessarily follow that stop and search activity does not reduce crime,” the study concludes.

It says that the study was based on data at London borough level with populations of over 200,000 per borough and it is possible that it masked localised efforts in cutting crime in particular areas: “It is possible that a base level of stop and search activity does have an effect after which there are diminishing, or even zero, returns,” but the researchers say it has not been possible to shed light on what the level would be.

The home secretary clashed with the Met commissioner over the issue last October when she publicly criticised his claim that the rise in stabbings was linked to falls in stop and search in London boroughs.

There has been a significant reduction in the use of stop and search by the police in England and Wales, down from a peak of 1.2m in 2010/11 when 9% led to an arrest to 539,000 in 2014/15 of which 14% resulted in an arrest. Knife crime has fallen by more than 16% since 2011 although that includes a 9% increase recorded by the police in the last 12 months.

A Home Office spokesperson said: “The government is clear that the power of stop and search, when used correctly, is vital in the fight against crime. However, when it is misused, stop and search is counterproductive and a waste of police time.

“Stop and search must be applied fairly, effectively and in a way that builds community confidence rather than undermining it. No one should be stopped on the basis of their race or ethnicity.”



He added a number of new measures had been introduced since 2014 to improve the effectiveness of stop and search including the Best Use of Stop and Search scheme, which was creating more transparency and accountability in its use.



