Britain's intelligence agencies are helping the US investigate whether Covid leaked from a Chinese laboratory, The Telegraph has learned.
The move comes after US President Joe Biden ordered American intelligence officials to "redouble" their efforts to identify the origins of the virus and report within 90 days.
Biden ordered the review after claims by leading Western scientists that the virus was man-made and not transmitted by animals as originally claimed.
British intelligence officials have conducted their own investigation into the origins of the pandemic after claims Covid came from a laboratory in China – a claim the Chinese government has consistently denied.
On Friday night (Saturday NZT), Sir Richard Dearlove, a former head of UK intelligence agency MI6, said the situation was becoming an "intelligence issue" where British security services may need to "incentivise" Chinese defectors to get to the truth if China did not open up its research to scrutiny.
Britain's official position is that claims the virus leaked from a laboratory in the city of Wuhan, where the pandemic began, should not be discounted.
A senior Whitehall security source confirmed British intelligence officials are co-operating with the new American investigation in an attempt to establish the truth about the pandemic.
"We are contributing what intelligence we have on Wuhan, as well as offering to help the Americans to corroborate and analyse any intelligence they have that we can assist with," said the source.
"What is required to establish the truth behind the coronavirus outbreak is well-sourced intelligence rather than informed analysis, and that is difficult to come by."
Britain, together with the US, has been highly critical of an investigation carried out by the World Health Organisation into the origins of the outbreak, claiming China deliberately withheld access to data and samples when a WHO team made a four-week visit to Wuhan in January.
On Friday night, it emerged that leading scientific journals including Nature Medicine declined to publish evidence showing the virus might have been engineered in a lab.
Letters seen by The Telegraph show last April vaccine specialists contacted several journals over concerns structural details in the virus which looked man-made were being ignored, as well as pointing out flaws in previously published papers which suggested a natural origin.
Despite finding no fault with the analysis, Nature Medicine declined to publish the work, telling the authors there were many other "pressing issues of public health and clinical interest that take precedence".
The Journal of Virology and the biology preprint server BioRxiv also turned down the work, even though one eminent professor told The Telegraph in confidence: "The paper seems good to me and the conclusions, whilst startling, seem valid."
Dearlove, who has consistently said a lab escape of an engineered virus is a likely scenario for the outbreak of coronavirus, said it was "outrageous" that journals had failed to publish reports from leading scientists that challenged the standard view.
"It seems to me there has been absolutely no scientific debate," he told The Telegraph. "The Chinese made an assertion without any explanation and that the majority of the scientific community seem to accept it at face value. It's clear that they've run an information operation to try and suppress any other view.
"Some scientific journals absolutely refused to publish anything that disagreed with the Chinese view. I put Nature at the front of the queue, Nature has been absolutely outrageous in the way they have co-operated with the Chinese narrative.
"This is the biggest disruptive event globally since World War Two. It's huge. We sit there and we take at face value what the Chinese say, and what I'm advocating is an absolutely clear debate and a proper discussion, and not complete suppression.
"If it did come out of the lab it raises all sorts of questions about virological research, and the mere fact this has happened and disrupted all the world's economy, what does that say to an aggressive malign regime who might want to go mucking around with a virus?"
Scientists' call for independent inquiry
Earlier this month, 18 of the world's top epidemiologists and geneticists wrote a letter in the journal Science calling for an independent inquiry into the lab leak theory.
Dearlove said scientists who did not want to align themselves with the Trump administration were now coming forward after Biden's call for an inquiry.
"Nobody wanted to associate themselves with Trump, and now you've got Biden they've all literally switched sides," he added. "Now, suddenly, the dam has broken.
"I sent this material to Porton Down a year ago and what infuriates me is that a year ago people refused to listen to us. Over the last year anyone who thought that has been accused of being a conspiracy theorist, and told you don't know what you're talking about."
The paper turned down by Nature Medicine was written by Professor Angus Dalgleish, foundation professor of oncology in the Institute of Infection and Immunity at St Georges, University of London, and Birger Sorensen, one of the world's leading vaccine designers.
It included a research review highlighting how Chinese scientists had spent more than a decade conducting "gain of function" experiments to make bat viruses more deadly to humans, so they could get a head start on emerging diseases.
They pointed to inserts in the coronavirus genome that appeared to be evidence of this activity.
Evidence 'still points to natural origin'
On Friday night, Nature said publication was based on the weight of evidence, which still pointed towards a natural origin for the virus.
Dr Madelena Skipper, the editor-in-chief, said: "We make decisions based on the strength of conclusions. Of course we want to understand how the virus evolved, where it originated from.
"But we are very much in the middle of the pandemic. I would say right now the real question is to deal with the pandemic, the infections, the deaths, rolling out the vaccination.
"To the best of my knowledge the theory that it is a man-made virus is not being discussed. We are not calling for the debate to be shut down. Nobody is claiming this is a shut case, so we have written in our pages that we ought to continue to look into the origins of the virus.
"A breakthrough that would robustly demonstrate the origin of the virus would be something every journal would want to publish."
On Friday, Lawrence Young, professor of molecular oncology at Warwick University, said there were still unanswered questions about a lab leak and "a lot of concern" among scientists that the WHO's investigation was not detailed enough.
Young told BBC Radio 4's Today Programme: "They were not given access to any of the primary data within that laboratory. It feels too much of a coincidence, doesn't it, that the original cases were detected in Wuhan and what you have there is a very large centre working on coronaviruses."