Media playback is unsupported on your device Media caption MI6 officer Gareth Williams was found dead at his London home in 2010.

A leading pathologist says the possibility MI6 officer Gareth Williams died alone should be re-examined.

Dr Richard Shepherd told the BBC there is "credible evidence" that bags identical to the one Mr Williams was found in can be locked by someone inside the bag.

Expert witnesses at the inquest into Mr Williams' death failed to do so despite making hundreds of attempts.

However, evidence has since been published claiming it can be done.

Image caption Gareth Williams was found dead locked in a bag in his home in 2010

Dr Shepherd, who conducted one of the post-mortem examinations of Gareth Williams, has previously worked on other high profile cases including the deaths of Princess Diana and the government scientist David Kelly.

He says the police should now re-examine the possibility Mr Williams died alone as part of their on-going investigations.

Speaking to Radio 4's The Report, he said: "Now that we have credible evidence that it is possible to lock the bag from the inside, whilst it doesn't rule out homicide, clearly the chances of this as a solitary sexual act have to be considered in any future investigation by the Metropolitan Police."

The Metropolitan Police said the circumstances of Gareth Williams' death continue to be the subject of a thorough investigation.

Mr Williams was found dead, locked in a bag located in a bath tub in his London flat in 2010. One key question before the inquest into his death was whether he had locked himself in the bag.

At the pre-inquest hearing, coroner Dr Fiona Wilcox said the question was central to her inquiries.

Confined space expert Peter Faulding told the inquest that while he could not rule out that it was possible, "even Houdini would have struggled with this one".

A second expert, William MacKay said he and an assistant had also failed despite making more than a hundred attempts.

Their evidence helped the coroner Dr Wilcox earlier this month come to the conclusion that Mr Williams was probably unlawfully killed.

New evidence emerges

However, journalist Claire Hayhurst claims she managed to lock herself in a similar bag after just five attempts under the guidance of a former soldier, Jim Featherstonhaugh, who claims to have figured out a technique.

"The trickiest part was getting the lock together which is the biggest riddle of it. I spent maybe two-and-a-half hours getting in and out, filming it, and most of that time was spent with me outside the bag desperately drinking water and trying to recover," she told the BBC.

"I'm not super-fit but I've been told I've got a similar build to Gareth.

"I'd agree that someone of exactly the same proportions would be a fairer comparison but I do think me doing it shows that it's certainly possible."

Claire Hayhurst stresses she worked under the supervision of safety experts and says any attempt to recreate the experiment would be highly dangerous.

Confined space expert Peter Faulding told The Report he stood by the evidence he gave to the inquest.

"None of my conclusions were wrong - a young girl zipping a bag doesn't discredit this inquiry whatsoever," he said.

"We were fully aware of other methods of being able to lock the bag but she or nobody could achieve it without leaving her DNA on the bath - and that's the key to this," he added.

It has also been pointed out that Claire Hayhurst did not lock the bag in exactly the same way as the holdall found in Gareth Williams' flat.

At the inquest into his death, Dr Fiona Wilcox said she was satisfied that a third party had been involved in moving the bag containing the MI6 officer into the bathroom of his flat.

Hear more on The Report on BBC Radio 4 on Thursday, 24 May at 20:00 BST.

You can listen again via the Radio 4 website or by downloading the podcast.