Spy found dead in bag may have had a fetish for confined spaces

Detectives are investigating whether the code-breaker, whose naked body was found inside a zipped and locked holdall, was a fan of so-called "claustrophilia".

Mr Williams, 31, is thought to have died accidentally from a lack of oxygen after he agreed to be locked inside the red 32-inch long North Face bag by another person. One possibility is that the sex game went tragically wrong and the second person returned to find Mr Williams had died. The man — or woman — then fled the Pimlico flat, not leaving any forensic clues.

Police are now concentrating on Mr Williams's private life which detectives are convinced holds the answer to how he died. An examination of the spy's two laptops found in the flat showed he visited websites on claustrophilia, a desire to be confined in closed spaces.

There were also said to be links on one computer to a bondage and sado-masochistic website.

The development emerged as Scotland Yard announced that tests on the MI6 employee's body revealed no traces of any alcohol, drugs or poisons that may have caused his death.

Mr Williams's decomposing body was found in the padlocked holdall in the bath of his flat on August 23. The spy was last seen eight days before his body was found and detectives believe he may have lain undiscovered for several days. CCTV showed him shopping at Harrods and at Holland Park Tube station. There were no injuries to his body and nothing in the flat that suggested a struggle or forced entry.

A post-mortem examination has been unable to find a cause of death but it is possible he died from a combination of suffocation or dehydration, which is difficult to identify.

Police do not believe that he was able to lock himself into the North Face bag on his own and suspect at least one other person was inside the flat at the time.

They are still trying to trace a couple, both of Mediterranean appearance and aged between 20 and 30, who had paid a visit to Mr Williams's flat about a month before he was found dead. Despite repeated appeals they have not come forward.

A colourful wig and women's make-up were also found inside the flat, but detectives can find no evidence that Mr Williams was a cross dresser. Sources say he was an intensely private individual who appears to have gone to great lengths to hide details of his private life.

Mr Williams, a keen competitive cyclist, was on a year's secondment to MI6 from GCHQ, the Government's electronic eavesdropping agency in Cheltenham.

Coroner Dr Paul Knapman is due to review the case in private next Wednesday.

A Metropolitan Police spokesman said: "Results from comprehensive further toxicology tests carried out in relation to the death of Gareth Williams have come back negative, showing no trace of any drugs, alcohol, poisons or any other substances that would indicate cause of death.

"There are no plans to carry out any further tests of this type, but inquiries continue to try to establish a formal cause of death. Mr Williams's death remains suspicious and unexplained and enquiries into the circumstances continue."