Evidence is continuing to mount that the Chinese government systematically concealed the extent of the coronavirus outbreak in Wuhan.

On the BBC’s Panorama programme tonight, Professor Yuen Kwok-Yung, a Hong Kong University microbiologist turned whistle-blower and one of the world’s top coronavirus experts, will describe how the actions of the Chinese authorities before the Wuhan lockdown suggest a “cover-up”.

Within China, the official version of events is that when clear evidence emerged of human-to-human transmission the information was immediately made public and the authorities implemented stringent control measures, including the lockdown of Wuhan on January 23.

Yuen’s testimony confirms that the authorities possessed substantial evidence of inter-human transmission much earlier than is claimed.

On January 12, Yuen diagnosed a family in Shenzhen, a city 700 miles from Wuhan on China’s south coast, with the novel coronavirus. The fact that not all of them had travelled to Wuhan prompted Yuen to immediately contact the authorities.

Yuen also describes how he visited the “wet market” in Wuhan suspected of being the source of the new virus, but discovered it had already been thoroughly cleaned before scientific evidence could be collected.

Yuen says: “You may say that the crime scene was already disturbed. Because the seafood market was cleared we cannot identify the animal host which is giving the virus to humans… I do suspect that they [the Chinese authorities] have been doing some cover-up locally in Wuhan.”

China’s government has always maintained that its handling of the outbreak has been “open, transparent and responsible”. Yuen’s testimony is the latest in a long stream of evidence undermining this claim.

In April, it was revealed that the government was stringently policing the publication of coronavirus research papers. Throughout the pandemic an army of internet censors have scrubbed social media clean of inconvenient information and added comments retrospectively to suggest that those in power were engaging with concerns about the virus.

As far back as December doctors, scientists and hospital staff have been arrested and silenced after speaking out about the severity of the outbreak. The highest profile case was of Dr Li Wenliang who was reprimanded for warning the world about a strange new virus and forced to sign a statement denouncing his alert as an “unfounded and illegal rumour”. Li would later die after contracting coronavirus.

Chinese citizens who highlight facts which are in opposition to the official narrative continue to disappear.

When questioned about the muzzling of scientists at the start of the outbreak, Professor Li Lanjuan, a senior Chinese government adviser, told Panorama: “To announce its contagiousness, if it is not yet confirmed, would cause public panic. Therefore, we must be responsible to the public, and ascertain the facts first.”

But the fact remains that China was detaining people for “spreading rumours” about the virus more than three weeks before the Wuhan lockdown.

The origins of and response to the virus are particularly sensitive topics in Beijing. Professor Steve Tsang, director of the SOAS China Institute, said:

“In terms of priority, controlling the narrative is more important than the public health or economic fallout. It doesn’t mean that the economy and public health aren’t important. But the narrative is paramount.”

Further revelations are sure to emerge over the coming months and calls for an international investigation into China’s handling of the crisis will intensify. As the world continues to demand answers, whistle-blowers like Yuen will help to paint a more detailed picture of what really went on in those first crucial weeks.