This newspaper used Freedom of Information rules to obtain a cache of 32 emails about a secretive teleconference between British and American health officials held early in the pandemic.
But officials blacked out almost every word before releasing the crucial documents.
Before this discussion, several of the world's most influential experts believed the new virus most likely came from a laboratory - but days later, the scientists began dismissing such scenarios as 'implausible' and branding them conspiracy theories.
The Mail on Sunday requested emails, minutes and notes on the call between Sir Patrick Vallance - Britain's chief scientific adviser - and its organisers Sir Jeremy Farrar, director of the Wellcome Trust medical charity, and Anthony Fauci, the US infectious diseases expert and presidential adviser.
Yet when the documents were released they had page after page redacted with thick lines of black ink by Whitehall officials. Even the names of experts copied in on discussions were blocked - and exchanges as trivial as one Edinburgh biologist's 'thank you' for being invited - leaving only a few basic details about the call visible.
The lines left intact include a demand for the discussions, involving 13 participants around the world, to be conducted in 'total confidence', and an intriguing email line suggesting 'we need to talk about the backbone too, not just the insert'.
That was possibly sent by Dutch virologist Marion Koopmans, a member of the World Health Organisation team that produced a widely criticised report into Covid's origins.
Such absurd state secrecy is highly contemptuous towards taxpayers and to a world that wants to know what caused this devastating pandemic to guard against similar catastrophes in the future.
'This is a matter of massive public and global importance,' he said. 'It is hard to see why there should be such secrecy that it outweighs the immense public interest and requires them to redact this sort of important data.'
He is right. Such official obfuscation only serves to fuel concerns over a possible cover-up on Covid's origins - and about Britain's strange silence on issues of such global importance, which surprises some close international allies. I began attempting to obtain details of Government notes and discussions with key participants at the start of August, yet these derisory blacked-out pages are all I have winkled out of Whitehall so far.
A request for emails, notes or transcripts of Vallance's conversations with Farrar on origins of Sars-CoV-2 (the strain of coronavirus that causes Covid-19), Wuhan Institute of Virology or Shi Zhengli, its infamous 'Batwoman' expert, was rejected on cost grounds.
The Government confirmed, however, that 'we hold the information that you have requested'.
'This all begs an obvious question, just as with China's secrecy: why would officials not share such information if there was nothing to hide?' said Tory MP Bob Seely, a member of the Foreign Affairs Committee.
Perhaps this is down to arrogant politicians and an army of aloof civil servants who believe the public does not have the right to know what is being done in their name.
Tony Blair flipped from supporting Freedom of Information rules when in opposition to saying 'I quake at the imbecility' of the idea when his government made them law, his memoirs revealed. And there has been a sharp rise in refusals to grant requests since the Tories took power in 2010.
Yet surely the origins of the pandemic, an event that has caused such disruption and misery to so many, is of utmost public interest - even if the implications might be profound for our relations with China or the unfettered pursuit of science?
The pivotal role of this teleconference on February 1 last year emerged from emails obtained in the US and a recent book on the pandemic by Farrar. Two days before the call, the WHO had belatedly raised the alert level on the unfolding public health disaster.
The teleconference was led by Farrar, an expert on infectious diseases, who admits that he saw the 'huge coincidence' of a novel coronavirus erupting in 'a city with a superlab' that was 'home to an almost unrivalled collection of bat viruses'.
Many prominent scientists, including several participants on the call, feared the new virus looked engineered - among them California-based immunologist Kristian Andersen, who told Farrar beforehand he was alarmed by Covid's unusual properties.
He said the binding mechanism 'looked too good to be true, like a perfect key for entering human cells' while its furin cleavage site - a feature not found on similar types of coronavirus that allows it to enter efficiently into human cells - might be expected 'if someone had set out to adapt an animal coronavirus to humans by taking a specific suit of genetic material from elsewhere and inserting it.'
Farrar opened the discussion, which was then led by Andersen and Eddie Holmes, an Australian-based virologist who told the Wellcome chief before the call he was '80 per cent sure this thing had come out of a lab'. Yet after their conference call, these same experts played leading roles in efforts to dismiss such fears as conspiracy theories in science journals and on social media.
Comment: One wonders what they were told that made them change their minds so quickly.
Farrar admitted he was torn on the origins in a follow-up email to Fauci, yet signed a notorious Lancet article secretly organised by British scientist Peter Daszak days later that condemned 'conspiracy theories' alleging Covid was not natural, claiming they spread 'fear' and 'prejudice', while incredibly praising Beijing's 'open and transparent' sharing of data. Farrar also convened a hugely influential Nature paper by Andersen, Holmes and three others insisting 'any type of laboratory-based scenario' was not 'plausible'.
Comment: So the same guy who was conducting GOF research into coronaviruses pushed a paper labeling the lab-leak theory a conspiracy theory? Nothing to see here folks.
Comment: The gentleman doth protest too much.
Andersen, who deleted his combative Twitter account after emails emerged that exposed his earlier views, later said this was 'a textbook example of the scientific method' in which a preliminary theory was rejected as more information emerged. Yet there remains no evidence to show Sars-CoV-2 spilled over naturally from animals. So we need to understand why these experts changed their minds so fast and so decisively that they scorned people with views they had held themselves only recently.
This is why the Government's secrecy is both deplorable and dangerous, according to Gary Ruskin, head of the public health group US Right To Know that has exposed the activities of key experts including Daszak in this saga.
'Transparency is crucial to expose corruption, abuse of power and hidden conflicts of interest,' he said. 'Even in the US, which is weak in science transparency, we have been able to unearth documents useful in pursuing the origins of Covid-19. Such efforts seem impossible in the UK. That is regrettable - and subsequent generations may end up paying for it with their lives if we cannot use the tools of transparency to figure out how Covid-19 came upon us.'
It is, finally, accepted outside China there are two credible theories on the origins: natural spillover from animals, or some kind of laboratory incident.
Concerns over a possible research incident have grown as fresh evidence emerges about the risky work of Daszak, president of EcoHealth Alliance, and Shi, head of the Centre for Emerging Infectious Diseases at Wuhan Institute of Virology.
First, explosive documents detailing two grants in 2014 and 2019 to EcoHealth Alliance showed how the US was in effect outsourcing 'gain of function' work to China - even during a three-year period when it was banned in America.
The US supported the construction of new 'chimeric' Sars-related coronaviruses that combined a spike gene from one with genetic material from another - and the resulting creation could infect human cells and have more potential to cause disease.
So we now know beyond debate that speculative 'gain of function' experiments on mutant bat viruses were taking place in Wuhan laboratories - and in units that did not have top-level biosafety - despite Batwoman's vociferous denials.
Then a team of researchers known as Drastic obtained an astonishing proposal by Daszak for a US grant to study pathogens by creating infectious bat coronaviruses in a lab and inserting genetic features designed to boost their ability to infect human cells.
EcoHealth even proposed to work with Shi and another prominent US expert on introduction of 'appropriate human specific cleavage sites' into Sars-like viruses - an intriguing suggestion given the unusual cleavage site in Sars-CoV-2.
The $14.2 million (£10.5 million) grant bid was rejected. But did another funder pick up the proposal? At the very least, this proves the researchers were toying with precisely the sort of risky science that could have cooked up a virus eerily similar to the one behind the pandemic.
It is baffling that the US Congress has not demanded that New York-based Daszak, who led efforts to crush debate over a possible lab leak despite obvious conflicts of interest, appear under oath and disclose all his organisation's data.
But this all begs another question: why is our own Government redacting key documents and refusing to share information it holds on events that might help us grapple with the mystery of the pandemic's origins after almost five million deaths?