A Wuhan laboratory has reportedly been carrying out experiments on bats from the cave believed to be the source of the coronavirus pandemic.
The revelation has fuelled a conspiracy-like theory that the devastating virus may have originated from the Wuhan Institute of Virology via an accidental leak, rather than the city's live animal market.
The Mail on Sunday reports that that the Institute has been carrying out research on bats captured from caves in Yunnan, where the Covid-19 genome is thought to have come from.
The caves are 1,000 miles away from Wuhan, the Chinese city which is now infamous for having been the epicentre of the global coronavirus pandemic.
Scientists say it is highly likely that Covid-19 first came from bats, but first passed through an intermediary animal before jumping to humans.
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It is widely believed that the flu-like virus first began infecting humans in late 2019 after being transmitted from an animal at the Huanan seafood market.
However, UK government sources have told the Mail on Sunday that while "the balance of scientific advice" is still behind the animal market theory, an accident at the lab is "no longer being discounted".
The experiments, which relate to the origin of coronaviruses, are said to have been paid for by a $3.7m grant from the US government.
Funded by the US National Institutes of Health, the results of the research were published in November 2017 under the heading: "Discovery of a rich gene pool of bat SARS-related coronaviruses provides new insights into the origin of SARS coronavirus."
Scientists are uncertain about several aspects of the origin of Covid-19, with fresh doubts also arising last week following research by Cao Bin, a doctor at the Wuhan Jinyintan Hospital, which found that 13 of the first 41 diagnosed patients had not had any contact with the market.
However, responding to the claims, the Chinese Embassy has described speculation around the lab's activities as "hasty and reckless allegations".
In a letter also published in the Mail on Sunday, it says: "Hasty and reckless allegations, such as naming China as the origin in an attempt to shift the blame before any scientific conclusion, is irresponsible and will definitely do harm to international co-operation at this critical time.
"In his telephone conversation with Foreign Secretary Dominic Raab, State Councillor and Foreign Minister Wang Yi pointed out that 'alarmingly, some people are attempting to politicise the epidemic, label the virus and stigmatise China...
"Raab expressed the UK's firm opposition to politicising the Covid-19 outbreak and fully agrees with China that the source of the virus is a scientific issue that requires professional and science-based assessment."
