Silcott, serving life for the murder of boxer Anthony Smith in 1984, had hoped to overturn the conviction.

The Criminal Cases Review Commission, set up to investigate miscarriages of justice, refused.

Silcott has always claimed he was acting in self-defence when he stabbed Anthony Smith to death at a party in Hackney, north London.

Keith Blakelock: Silcott's conviction for his murder was quashed

He was convicted of the murder and sentenced to life imprisonment in January 1986, while still awaiting trial for the murder of Keith Blakelock during the riots at Broadwater Farm in Tottenham in the mid 1980s.

Although he was convicted of PC Blakelock's murder the following year, the conviction was quashed on appeal in 1991 amid fears that vital evidence could have been fabricated.

Silcott, who has already received around £17,000 compensation from the Home Office for a miscarriage of justice, had hoped to have his earlier conviction overturned and win his liberty.

Legal aid

Evidence submitted to the CCRC included statements from new witnesses backing up Silcott's claims that Smith was armed with a knife and had appeared to threaten Silcott.

Silcott has already been refused leave to appeal by a single judge in March 1988 and by the full Court of Appeal in December 1988.

Silcott has also been granted legal aid to sue the Metropolitan Police for damages over the investigation into the Blakelock killing. He is reportedly seeking £200,000.

The CCRC had been considering Silcott's case since it was set up by the Home Office in 1997.

A case is only referred back to the Court of Appeal if there is a "real possibility" of a conviction being quashed.

This is the 77th decision by the CCRC not to refer a case back.

The evidence put before the Commission included claims that Smith was the leader of a criminal gang which was terrorising north London.

Fabricated confession

Smith had reportedly picked a fight with one of Silcott's friends a few days before his death.

When Silcott intervened, Smith allegedly threatened to kill him, and it was a fear that this threat was being carried out which prompted Silcott to arm himself on the night Smith died.

Silcott's conviction for the Blakelock killing was quashed after scientific tests showed his confession had been fabricated.