Covid is most likely to have come from a lab leak in China, the professor behind a virus symptom tracker has said.

Prof Tim Spector, who helped create the Zoe symptom tracker app and was awarded an OBE for services in the Covid-19 response, told a podcast that it was "obvious" there had been a cover-up about the origins of the pandemic.

The virus emerged near the Wuhan Institute of Virology in December 2019, where scientists had been experimenting with bat coronaviruses.

Claims that the virus may have leaked from the lab were dismissed by some scientists as a racist conspiracy theory.

Speaking on the Zoe podcast, Prof Spector, a professor of genetic epidemiology at King's College London, said: "I don't think there's any doubt that this virus emanated in China, in a place near Wuhan.

"The question is, did this come from bats? Did it come from a lab that was working on this virus and manipulating it to make it grow faster? Or was it a totally artificially generated virus to cause harm that they then didn't control?

"The initial ideas and the government's official response was that this was related to bats and was a natural phenomenon that came out of this market in Wuhan.

"It's looking increasingly like that was a bit of a cover-up and that the most likely source of this was a lab leak from Wuhan."

Prof Spector pointed to congressional hearings in the US that heard there had been collaborations between US and Chinese labs to study the infectiousness of coronaviruses and to look at how to "control them or speed them up".

An adviser to Downing Street during the pandemic, Prof Spector added: "That seems to be the most likely scientific answer for what went on that explains both the epidemiology, the timing.

"Also, the trail of shredded documents and email exchange between the US and China at the time. And it's also, there was a very obvious cover-up very early on by various governments saying we have to get a report out there saying this is all down to bats so people aren't going to blame labs and scientists to keep that credibility going.

"So that's my personal view and there are views on all sides of this.

"I don't think the idea that someone built a virus from scratch would be very easy to do. So I think it's more likely that was a mistake rather than anything deliberate, but I think these were people working with hazardous viruses that got out of control rather than it being a plot."

Wuhan Institute of Virology (WIV) embarked on "gain of function experiments" in 2010, to increase the infectiousness of Sars coronavirus in humans.

By 2015, the scientists had created a highly infectious chimeric virus that targeted the human upper respiratory tract.

In 2018 and 2019, grants from the National Institute of Allergy and Infectious Diseases in the US showed Dr Shi Zhengli had applied to work on "virus infection experiments in humanised mice" using Sars coronaviruses to find out what changes could lead to a spillover event into humans.

Alina Chan, a scientist at Harvard, told MPs at the House of Commons science and technology select committee: "You find these scientists who said in early 2018: 'I'm going to put horns on horses,' and at the end of 2019 a unicorn turns up in Wuhan city."

Freedom of information requests revealed Wuhan researchers collected bat coronaviruses from China and south-east Asia.

These were sent to various laboratories hundreds of miles away for "sequencing", "archiving", "analysis" and "manipulation".

WIV had collected more than 220 Sars-related coronaviruses, at least 100 of which were never made public.

Members of staff were also photographed wearing inadequate levels of personal protective equipment while handing bats.

Last year, the WIV was stripped of US funding for 10 years for conducting dangerous experiments, which increased the potency of coronaviruses before the pandemic.

Prof Spector said that the case had shown that labs across the world should face more oversight and be treated with the same seriousness as a nuclear threat.

"If that is the most likely solution, well that could happen again in another lab if we're not careful," he added.