Police forces with some of the worst records of targeting black people have decided to stop recording the ethnicity of the people their officers stop and ask to account for their movements, the Guardian has learned.

Five out of the 10 forces most likely to use stop-and-account powers disproportionately against black people – West Midlands, Avon and Somerset, Thames Valley, Sussex and Hertfordshire – have halted recording the race of people they have stopped. They have used a government change in the rules introduced in March, which was aimed at cutting bureaucracy.

In total, 21 out of 43 forces in England and Wales will stop recording details, according to responses to requests under the Freedom of Information Act.

A high court challenge is being brought over the decision.

The collection of data about the race of people stopped is one of the key legacies of the 1999 Stephen Lawrence inquiry into police racism. The figures have shown that black people are more likely to be subject to the powers, and those figures have been used to pressure the police into cleaning up discrimination in the ranks.

New totals show that the worst offender is the West Midlands force, which is seven times more likely to stop an African-Caribbean person than a white person. The force, Britain's second biggest, is one of those that has decided to stop recording the ethnicity of people subjected to stop and account by its officers.

According to analysis by Dr Michael Shiner of the London School of Economics, there are wide variations in how much more likely different forces are to use stop-and-account powers against black people. . Some do not appear to be discriminating.Among those ceasing the recording of ethnicity, But

Gwent has the second highest disproportionality rate of five times, while African-Caribbean people in West Mercia, Avon and Somerset and Warwickshire are all roughly three times more likely than their white fellow citizens to face stop and account.

Shiner, who prepared his data for Stopwatch, which campaigns for fairness in police stop powers, said: "Figures such as these may be a source of embarrassment to the police. Getting rid of recording may relieve the embarrassment but prevents us from dealing with the problem."

A UN committee this month warned that the changes could "encourage racial and ethnic stereotyping" among officers.

Stop and account is the most commonly used power by officers to question people in the street. In 2008-09, the last year for which official figures are available, there were 1,126,258 stop and searches compared with 2,211,598 stop and accounts.

One experienced officer said colleagues could use the power, which does not require reasonable suspicion of criminality, to justify searching someone, which does: "It could lead to a suspicion to arise. Why are you not talking to me? Why aren't you answering questions?"

Forces will continue recording the race of people stopped and searched, with officers arguing that in a time of limited resources, it is better if the money is spent on that rather than on collecting data from stop and account.

Three forces who have ended recording the data – Hampshire, Thames Valley and Hertfordshire – will feature in a test case brought by Hugh Diedrick, an electrical engineer, who says he has been subjected to various stops as he travels around the country for work. In one incident he claims to have been strip-searched and in the latest, in July 2011, he alleges that Hertfordshire officers picked on him because of the colour of his skin in order to subject him to a stop and account.

The legal case will assert that the decision by police forces to stop recording the ethnicity data was taken without proper consultation and will break their legal obligations to ensure equality.

Sarah McSherry, the solicitor bringing the high court claim, said: "These statistics can help chief constables tackle potential racism. But scrapping these figures smacks of a complete lack of will to tackle discrimination, which has affected many people, such as my client, Mr Diedrick."

The decision to record the ethnicity of people subjected to stop powers was a key recommendation of the inquiry into police failings that allowed the killers of Stephen Lawrence to escape justice.

The Macpherson report said anyone stopped by the police should be given a record stating the reason for the stop, and their ethnicity should be recorded. That came into force in 2005, but police claimed it was too time-consuming.

Dr Rebekah Delsol of the Open Society Justice Initiative said: "Cutting one of the few mechanisms for accountability at this time – of all times – is reckless and irresponsible as it risks fuelling the tensions that have scarred police-community relations for 30 years."

Craig Mackey, who leads for the Association of Chief Police Officers on stop-and-search issues, told the Guardian: "The premise that somehow forces chose to discontinue the recording of ethnicity as part of stop and account on the basis of hiding some sort of practice, there is absolutely no evidence of that whatsoever."

Mackey added that stop and account was not really a police power and that people could ignore requests for information from an officer.

The assistant chief constable of Thames Valley police, Richard Bennett, said: "In common with most other forces, we no longer record stop-and-account activity following the removal of the mandatory national requirement."

The Home Office said: "From 7 March 2011 we have removed the national requirement to record stop and account, in order to reduce police bureaucracy. "These changes will save hundreds of thousands of hours of police time."

A report from the United Nations committee on the elimination of racial discrimination condemned the changes, warning: "The committee is concerned that these measures may not only encourage racial and ethnic stereotyping by police officers but may also encourage impunity and fail to promote accountability in the police service for possible abuses."