Sir Richard Dearlove, who headed the British secret intelligence service between 1999 and 2004, said it would now be difficult to prove the Wuhan Institute of Virology was working on experiments to make a coronavirus that would be more deadly to humans.

Speaking to The Daily Telegraph's Planet Normal podcast, he also said the West had been naive in trusting China, which had infiltrated scientific institutions and journals in the UK and elsewhere.

Sir Richard said it was possible Chinese scientists who wanted to speak out about any coronavirus experiments had been "silenced".

"The People's Republic of China is a pretty terrifying regime and does some things we consider unacceptable and extreme in silencing opposition to the official line of the government," he said.

"We don't know that's what's happened, but a lot of data have probably been destroyed or made to disappear so it's going to be difficult to prove definitely the case for a 'gain of function chimera' being the cause of the pandemic."

Sir Richard said he felt some vindication as more people were beginning to take seriously his repeated questioning of the origins of the coronavirus. He spoke of "extraordinary behaviour" in the scientific community which had "shut down any debate" and which he said verged on "academic bullying".

China, he said, had originally been "let off the hook" on questions about the virus's origins due to scepticism over the Trump administration, which had led such inquiries initially.

But after US President Joe Biden last week called for more investigations into the origins of Covid-19, and as British intelligence assists American counterparts in probing a possible lab leak, Sir Richard said the "whole argument" had now shifted.

But he also castigated parts of the West, including former Prime Minister David Cameron and First Secretary of State George Osborne, for "sheer naivety" in placing too much trust in China.

"Some of the things that were said by George Osborne and David Cameron about our relationship with China - how we were going to have this privileged position - I was staggered at the time by the sheer naivety that they could develop a relationship with China without understanding they were dealing with a communist dictatorship, and one that has its own strategic agenda," he said.

Sir Richard also said the World Health Organisation was "a lost cause" and should not be left to look rigorously into the origins of the virus to provide "a clear understanding of what the hell happened".

Australian Associated Press