Stop-and-search powers proposed by the Home Office risk “perpetually criminalising” previous offenders, rights groups have warned. In a letter to the home secretary, Priti Patel, the groups say the move is “disproportionate and unnecessary” and that the Home Office’s own research has suggested that higher search rates may have no discernible crime-reducing effects. The proposal was designed to meet the Conservatives’ 2019 manifesto pledge to make it easier for officers to stop and search those convicted of knife crime. The government is also exploring the possibility of making it an offence to fail to cooperate with a search while subject to a serious violence reduction order (SVRO). Organisations including StopWatch, Inquest, Open Society Foundations, Liberty and a number of experts said in the letter that research shows that widening police powers further increases racial disparities in stop-and-search practices. It said: “The use of stop and search is heavily concentrated on black and minority ethnic groups – government figures show that black people are searched at 8.9 times the rate of white people. “These disparities are reproduced throughout the criminal justice system; in arrests, out-of-court disposals, prosecution and sentencing. Years of policing research tells us that when discretion in the use of police stop and search is increased, racial disparities worsen.” Under existing section 60 powers to search individuals without suspicion in areas where there are fears of serious violence, research shows that black people are searched at more than 40 times the rate of white people. The proposals to introduce stop-and-search measures without reasonable suspicion would further undermine the safeguard, the letter said, after previous efforts were ruled unlawful in 2010 by the European court of human rights. The consultation on the proposals ends on Sunday. StopWatch’s spokeswoman, Lucy Bryant, said: “The orders not only ignore, but run counter to a substantial body of evidence that shows stop and search has little, if any, effect on violence. Successful public health approaches provide a clear template, and yet these lessons about crime prevention and public safety have been overlooked. “What these powers will do is perpetually criminalise those who receive them, only making it harder for them to make positive changes, locking them into the very patterns of behaviour we hope to prevent.” A Home Office spokesperson said: “Our proposals aim to transform the way stop and search is used by targeting the small number of the most serious and persistent criminals. “They could take more knives and those who repeatedly carry them off our streets. Extensive safeguards are in place to ensure stop and search is done fairly and proportionately.” In its consultation document, it said that SVROs would give police the automatic right to search those already convicted of certain knife crime offences. “These searches could take place without suspicion so that these known criminals could be stopped at any time,” the Home Office document said. “SVROs would empower the police to stop and challenge those who are known to carry knives.” It added that although some rates of serious violence crime had stabilised, the overall figures were too high and there had been an increase in cases involving people who have already committed one offence involving a knife or other offensive weapon. The proposals come after the Guardian revealed that the Home Office dropped plans to improve the best use of the stop-and-search scheme, which were aimed at reducing “no suspicion” searches, and withdrew from consultations at the end of 2017. Patel then appeared to scrap the scheme altogether after it was announced in August last year that she would “lift all conditions in the voluntary best use of stop-and-search scheme over the use of section 60” in an attempt to crack down on violent crime.