Sir Mark Rowley told the London Assembly Police and Crime Committee that the errors made by detectives after the 1993 killing caused irreparable damage.

"The sad truth is that if you do such a bad job at an investigation in its first weeks and months you lose evidence... some of it can never be recovered," Sir Mark said.

"You miss forensic opportunities. You miss witness opportunities and witnesses' memories degrade.

"I don't want to pretend that you can necessarily always catch up [on] the grounds that you've so badly lost in the early days," he added.

"That's what makes it so egregious and makes the error so egregious that they're not repairable always.

"And some really top detectives have moved heaven and earth to try to cover some ground and have made some progress but haven't been able to recover it all.

"I always keep hoping that we'll find a new opportunity, but I'm not going to promise that we definitely will because I can't."

Stephen Lawrence was killed by a gang of five or six racist attackers in Eltham, southeast London, as he made his way home with his friend Duwayne Brooks in April 1993.

Just two of the murderers have faced justice - Gary Dobson and David Norris were finally jailed for life in 2012 after a trial that relied on tiny traces of forensic evidence.

The BBC named a sixth suspect in the case for the first time last month and outlined the bungled handling of the evidence against him.

Two witnesses said a man called Matthew White had confessed to being present during the attack. He died in 2021.

One of the witnesses, White's stepfather, was not spoken to by police until 20 years after the murder because officers had previously misidentified him.

Stephen's mother Baroness Doreen Lawrence said she was furious that White would never face justice because of police mistakes.

A forensics review of any potential new evidence in the case is being led by Deputy Assistant Commissioner Matt Ward, who has recently joined the Met from West Midlands Police, but the murder investigation remains inactive.

Prosecutors have not yet decided whether officers involved in the original investigation should face charges for misconduct in public office.