The mother of Stephen Lawrence has said she has only ever found one police officer worthy of her trust in the last 26 years – and his bosses ousted him from his job.

Doreen Lawrence was giving evidence to MPs on the home affairs committee who have been investigating what progress has been made in the 20 years since an official report exposed police prejudice.

The Macpherson report in 1999 found that police blunders that had helped the killers of Stephen Lawrence escape justice were in part due to prejudice caused by institutional racism, with Lady Lawrence telling MPs on Tuesday that it “still exists”, 20 years on.

Stephen Lawrence was stabbed to death in April 1993 in south-east London by a gang of at least five white youths. Two, Gary Dobson and David Norris, were eventually convicted and jailed but others remain free.

Lady Lawrence told MPs of her 26 years of experience of the police and said: “The only officer I really trusted, who got the two convictions, and they got rid of him, they made him retire when he did not want to.”

The officer was former DCI Clive Driscoll who led the murder hunt that resulted in the conviction of Dobson and Norris in 2012.

The police vowed to change after the Macpherson report but some within their own ranks say not enough has been achieved.

Lawrence said after her son was murdered police had failed the family: “We were treated like we were the criminals, not the victims.”

She said officers and young people lacked respect for each other. She had witnessed encounters on the street in which she felt police were heavy-handed. “I still feel that police on the beat just don’t get it. I would drive past, walk past, and I see one individual, a young black man, he’d probably have about six officers around him. Do you need that intimidation, do you need that amount of officers? No, you don’t.”

She said efforts to stamp out racism in society have stalled. “It does seem as if things have become stagnant.”

Lawrence said the top priorities should be education and teaching children “true history”, such as how they came to be in this country. She said there needs to be more focus on the police and “how they police, because without consent they can’t police the community”.

“People … are still suffering from what we as a family went though back in 1993,” said Lawrence.

MPs also heard from black police officers who criticised the use of stop and search, rising as violent crime increases, and they also called for radical change.

Tola Munro, president of the National Black Police Association, said the law should be changed to allow positive discrimination for a limited time. The scheme was used in Northern Ireland to get more Catholics into the police.

Munro dismissed concerns that would lead to black officers being viewed as not up to the job by their white counterparts: “We get it anyway, you might as well be hung for a sheep as a lamb.”

Sgt Janet Hills of the Metropolitan Black Police Association, said she had been stopped when off duty, and while working had been mistaken by colleagues for a prisoner, rather than the arresting officer.

There are at least two active inquiries into the Lawrence case. In one the National Crime Agency is looking into claims that corruption also shielded the killers. The other is a judge-led inquiry into allegations that undercover officers spied on Lawrence and her family.

That inquiry has still not taken evidence three years after being set up, said Lawrence. “They’re still going through the paperwork.

“For me 25 years, coming up to 26 years, and this to be still going on, is unbelievable that any family should have to go through this.”

Lawrence added: “The undercover inquiry that’s happening now, the police are doing all that they can not to give the true facts of what happened.”