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.
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The scientist said antibody tests were in the final stage of validation and could be hopefully ready to use in "days rather than weeks".
He said: "We think the epidemic is just about slowing in the UK right now."
Officials are working 3.5million antibody tests ready to rollout nationwide.
Frontline health staff would be prioritised for those tests once they were ready, the government says.
However junior health minister Helen Whately told BBC radio: "I am not going to confirm when that's going to arrive."
The tests would then be rolled out to the wider general public, but chief medical officer Prof Chris Whitty said it would not be a "free-for-all" and those most in need would be prioritised.
Welsh minister for health and social services Vaughan Gething said: "The new antibody test will be a massive leap forward in helping us respond to coronavirus," he said.
"In the immediate term, it will help our critical workers - especially our frontline NHS and social care staff - return to work and provide life-saving care.
"This new test is vital to give them the confidence and keep them safe as they carry out their work to keep everyone else safe."
Currently medics who show symptoms of coronavirus are having to self-isolate but do not know if they've contracted the deadly virus.
It is hoped that the tests can give them certainty so they can go back to work.
Yesterday the death toll from Covid-19 rose by 209 to 1,019, and the confirmed number of cases increased to 19,522 - up 2,483 from the previous day.
