Scientists in Wuhan working alongside the Chinese military were combining the world’s most deadly coronaviruses to create a new mutant virus just as the pandemic began.

Investigators who scrutinised top-secret intercepted communications and scientific research believe Chinese scientists were running a covert project of dangerous experiments, which caused a leak from the Wuhan Institute of Virology and started the Covid-19 outbreak.

The US investigators say one of the reasons there is no published information on the work is because it was done in collaboration with researchers from the Chinese military, which was funding it and which, they say, was pursuing bioweapons.

The Sunday Times has reviewed hundreds of documents, including previously confidential reports, internal memos, scientific papers and email correspondence that has been obtained through sources or by freedom of information campaigners in the three years since the pandemic started. We also interviewed the US State Department investigators — including experts on China, emerging pandemic threats, and biowarfare — who conducted the first significant US inquiry into the origins of the Covid-19 outbreak.