The holdall death mystery of MI6 codebreaker Gareth Williams may never be solved, a coroner said.

Dr Fiona Wilcox criticised the 21-month investigation as she said it was "unlikely" the riddle "will ever be satisfactorily explained".

Dr Wilcox said it remained a "legitimate line of inquiry" that the secret services were involved in Mr Williams's death.

She ruled "it would appear that many agencies fell short" during the inquiries into his death.

But she said "there was no evidence to support that he died at the hands of" spies as the inquest drew to a close.

Despite a 21-month police inquiry and seven days of evidence, "most of the fundamental questions in relation to how Gareth died remain unanswered", she added.

She questioned why details of Mr Williams's private life were leaked to the press.

The coroner ruled out Mr Williams's interest in bondage and drag queens in having any bearing on his death, before adding: "I wonder if this was an attempt by some third party to manipulate the evidence."

Mr Williams, a 31-year-old fitness enthusiast originally from Anglesey, was found naked, curled up in the padlocked holdall in the bath of his flat in Pimlico, central London, on August 23, 2010.

Pathologists said he would have suffocated within three minutes if he was alive when he got inside the 32in by 19in red North Face bag. Poisoning and asphyxiation were the "foremost contenders" in solving the death riddle, they said.