Scotland Yard said yesterday they were urgently assessing an admission by David Norris that he was part of the gang of thugs who killed the 18-year-old student in 1993.
A Parole Board report said Norris had confessed to punching Stephen but he insisted he did not stab him.
An ex-senior Met police officer said he was sceptical and Norris must name others.
The report revealed the development on Thursday as Norris, 48, makes a bid for freedom after serving 13 years in prison.
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It raises the possibility the Met could reopen the case after shutting it down five years ago with up to four of the killers having escaped justice.
Asked about a new probe, a Met spokeswoman said it was too early to comment.
She said: "Our objective remains the arrest, prosecution and conviction of all of those responsible for Stephen Lawrence's murder.
"We are aware of the Parole Board report and will urgently assess its implications. We will keep the Lawrence family and their representatives updated as our work progresses."
David McKelvey, a former Met Chief Inspector, cautioned: "He's kept this secret for all the time he's been in prison but it's no surprise he's admitting this now because he wouldn't get parole otherwise.
"But he's only admitting to a minor part. If he was showing genuine remorse he'd be looking to speak to offi...