Police chief's memo signals reforms amid legal doubts over use of section 60 stop and search powers

Scotland Yard signalled on Thursday that it would significantly reform its use of the controversial power to stop people without suspicion, as an internal document by the Met police deputy commissioner, obtained by the Guardian, revealed fears that the courts could strike down such searches as unlawful.

The changes announced by police come days before a deadline set by the Equality and Human Rights Commission, which believes the use of "section 60" stop and search is unlawful. The watchdog had threatened court action over the power.

An African-Caribbean person is up to 27 times more likely than a white person to be stopped by police using those powers.

The Met said officers would be told to focus less on stopping people for small amounts of cannabis, and instead focus on those suspected of violent offences and carrying weapons.

The force aims to reduce by half searches for drugs where none are subsequently found.

As part of the reforms, senior officers will reduce by 50% the number of times they authorise an area to be the target of section 60 stops that do not require reasonable suspicion. They said more intelligence would be needed before this power could be deployed in the future.

The Met also said that the force's commissioner, Bernard Hogan-Howe, wanted the arrest rate from all stop and searches carried out to increase from 6% (at this rate  the lowest for an urban force) to 20%.

Police are facing a second legal challenge over their use of section 60, brought by a member of the public, Ann Roberts, who claims it is being used in a racist way against African-Caribbean people.

The 37-year-old special needs assistant, who has no convictions, was held down by officers on the floor in front of other people, handcuffed and taken to a police station where she was wrongly accused of being a user of class A drugs.

She claims that a disproportionate number of black Londoners are searched, in violation of article 14 of the European convention on human rights, which bans discrimination. In July the high court agreed she could bring a full legal challenge to section 60.

Craig Mackey, then the police national lead on stop and search, wrote to senior colleagues warning them of the development. Mackey is to become the new deputy commissioner of the Met.

In his memo addressed "to chief constables and commissioners", obtained by the Guardian, Mackey compared the legal challenge to section 60 to a successful challenge against stops made under section 44 of the terrorism act ? which was then struck down by the courts and scrapped by the government.

Mackey wrote: "Since the successful challenge was made in the European courts on the 'no suspicion' powers of stop and search, in section 44 [of the] Terrorism Act 2000, the potential for a similar scrutiny of section 60 powers has always been anticipated. Together with colleagues working in the field of stop and search, I have taken every opportunity to alert the police service to this potential development."

Hogan-Howe had indicated that he was willing to reform stop and search as evidence grew showing its use had been a factor in stoking the discontent behind the summer riots in England, and that the force had been unable to convince critics that the power's disproportionate use against ethnic minorities was not linked to racism.

The Met announcement did not include any direct measure to tackle disproportionality, however.

Commander Tony Eastaugh said the Met was listening to communities. "We know that young black and minority ethnic males aged 16-24 are over-represented as victims and suspects. If we get this right, using the right intelligence, we should see a positive outcome around disproportionality."

He added that section 60 stops without suspicion generated more resentment than stops requiring an officer to have reasonable suspicion: "Section 60 is the one people don't understand," he said.

Eastaugh said stop and search would focus more on violent crime.

As Britain's ethnic minorities are more likely to live in London than elsewhere the high use of stop and search in the capital skews the figure nationally.

John Wadham, of the Equality and Human Rights Commission, said: "We are pleased the force intends to change its practices so that fewer people are stopped without good reason, breaching their human rights."

Stop and search was also going to be an issue in London's mayoral election, with the former Met chief and Liberal Democrat candidate, Brian Paddick, planning to campaign on it.

Paddick said: "This is the first time a Met commissioner has said he is prepared to do something about stop and search. I have never heard anyone satisfactorally explain why the police are disproportionately stopping Asian and black people."