Antibody tests which can tell if someone has already had coronavirus or is immune to the killer disease could be available in "days".
Boris Johnson has previously described the tests as a "game changer" as they could potentially show who has immunity from the disease, which has killed more than 1,200 people in the UK.
Today Professor Neil Ferguson, told the BBC that the tests could be available within days. He said a third or even 40% of people do not get any symptoms, and up to 3% of the UK population had been infected.
The scientist said antibody tests were in the final stage of validation and could be hopefully ready to use in "days rather than weeks".