Police in England and Wales are being given greater stop and search powers to tackle rising knife crime.
Home Secretary Sajid Javid is making it easier for officers to search people without reasonable suspicion in places where serious violence may occur.
Campaigners said the move was “disappointing and regressive” and that stop and search is “not effective”.
Stop and search powers have been controversial for many years, with evidence that they are frequently misused and that they target black people disproportionately.
But Mr Javid said: “The police are on the front line in the battle against serious violence and it’s vital we give them the right tools to do their jobs.”
The change is being trialled in seven police force areas where more than 60% of knife crime occurs: London, the West Midlands, Merseyside, South Yorkshire, West Yorkshire, South Wales and Greater Manchester.
It makes it easier to use so-called “section 60” searches, where officers can search anyone in a certain area for a limited period of time to prevent violent crime
Under the new rules, inspectors will be able to authorise the use of section 60; currently, more senior officers have to give approval.
There will also be a lower threshold for authorising searches – police will only need to reasonably believe serious violence “may” occur, not that it “will”.
Section 60 has been used at large events such as Notting Hill Carnival last year and after violent incidents such as the stabbing of a man outside Clapham Common Underground station on Friday.
Other powers which account for the majority of searches will remain the same, and will still require officers to have reasonable suspicion of an offence.
With 285 deaths from stabbings in 2017-18, the most ever recorded, and a spate of high-profile killings this year, ministers have come under increasing pressure to tackle knife crime.
Metropolitan Police Commissioner Cressida Dick said officers in London had increased the use of section 60 over the past 18 months, following 132 deaths from stabbings in the capital during 2017-18.
She said: “Stop and search is an extremely important power for the police. It is undoubtedly a part of our increasing results suppressing levels of violence and knife crime.”
But Katrina Ffrench, chief executive of StopWatch, which campaigns against excessive use of stop and search, said: “This decision is a disappointing and regressive move, which is about politics not saving lives.”
Removing the need for reasonable suspicion “will not only exacerbate the racial disparity, but has the potential to further damage the relationship between the black community and the police,” she said.
A study for the College of Policing looked at ten years of stop and search data in London and found it to be “inconsistent” and “weak” as a deterrent.
In order to reduce violent crime by 2% in a borough during the following week, police would need to carry out 200 times the number of weapons searches, it said.
The extra powers roll back a key change made by Prime Minister Theresa May in 2014 when she was home secretary.
She introduced a revised code of conduct after an inquiry examined thousands of police searches and found 27% may have been illegal.
When misused, stop and search was “an enormous waste of police time” and “an unacceptable affront to justice”, she said.
Reflecting on the recent announcement, the prime minister said the powers were “an important tool in the fight against knife crime”.
Partly as a result of the 2014 changes, the use of stop and search fell in England and Wales from a peak of 1.4 million ten years ago to 277,378 last year.
The numbers of searches fell for every ethnic group, but ethnic and racial inequality has grown. In 2014-15 black people were four times as likely to be searched as white people, while in 2017-18, they were 9.5 times as likely to be searched.