Tests aim to reveal how MI6 spy died

Tests being carried out to establish whether the 30-year-old was poisoned, drugged or asphyxiated may not be completed until later next week and this will delay attempts by detectives to piece together exactly how he died.

A postmortem examination undertaken earlier this week proved inconclusive.

He was last seen alive eight days before his corpse was found stuffed in a bag at his apartment in Pimlico, London.

A confirmed sighting of Williams, who was on a year-long secondment from GCHQ, was made on 15 August in London, officers said. But police would not say whether the sighting was made on CCTV or came from another source.

The major investigation is being led by the Metropolitan Police's Homicide Command with the support of security-vetted Counter Terror Command unit SO15.

In an unusual series of counter-claims, Scotland Yard has strongly denied rumours circulated by the security services about his private life.

Sources within the intelligence community claimed that Williams was gay, had bondage equipment and paraphernalia associated with sado-masochism in his apartment and was linked to male escorts.

However, police have released statements saying the claims are unsubstantiated, sparking speculation that elements of the intelligence community have attempted to carry out a smear campaign against Williams.