Professor Neil Ferguson has predicted that Omicron Covid infections will probably peak in January if the Government does not act - and a fresh lockdown may be required.
The Imperial College London epidemiologist - dubbed 'Professor Lockdown' - told Radio 4's Today programme that the variant is likely to become the UK's dominant strain by Christmas.
Prof Ferguson said a new year lockdown is 'possible', although it depends on how much pressure the NHS faces in the coming weeks.
It comes after the UK recorded 101 new cases of the Omicron strain on Tuesday, bringing the total to 437 infections.
When pressed about the chance of a lockdown in the new year, Prof Ferguson said: "At the moment it's very difficult to rule out anything we really haven't got a good enough handle on the threat.
"If the consensus is it's highly likely that the NHS is going to be overwhelmed then it will be for the Government to decide what it wants to do about that but it's a difficult situation to be in of course.
"It (a lockdown) certainly might be possible at the current time."
The scientist added that early research suggests the virus is more resistant to vaccines than previous strains, however getting jabbed is still the best protection against serious illness and disease.
He said a laboratory-based South African study published last night indicated that Omicron can evade antibodies developed against the original strain better than any variant so far.
The professor also said research in the UK suggested protection from two doses of the Pfizer vaccine against mild disease roughly halved in Omicron cases.
He anticipated that case numbers, which are currently doubling every two to three days, will accelerate 'quite markedly' within a week or two.
Prof Ferguson said bringing back working from home rules could slow down the doubling of infections to four to five days.
Get all the latest news sent to your inbox. Sign up for the free Mirror newsletter
Last week, officials in South Africa, where Omicron was first detected, painted a bleak picture of the variant after cases rocketed and hospitalisations in the worst hit province rose by 300 per cent in two weeks.
One of the country's top medics said the country was facing an "unprecedented rise" in infections which appears to be driven by the mutant strain.
In the worst-hit province, Gauteng, average daily hospital admissions rose by 300 per cent in a fortnight.
