Doctors have called for face masks to be worn in restaurants and pubs to help halt the spread of the Omicron coronavirus strain.
The British Medical Association said there is only a small time period to act to get the variant under control.
It added the new strain, thought to be highly infectious, could have a "devastating impact" on the NHS .
There are mounting fears the variant may derail Brits' Christmas plans.
But Health Secretary Sajid Javid has dismissed calls for tougher restrictions.
Measures being introduced to try to combat the spread of the new strain include curbs on all arrivals to the UK.
In England, face coverings in shops and on public transport will become mandatory again from tomorrow.
Fines of £200 will reportedly be issued to those breaking the rules.
The penalties will double with each offence, up to a maximum of £6,400. The rules will not apply to the hospitality sector such as restaurants and pubs. British Medical Association boss Dr Chaand Nagpaul said: "The reintroduction of mandatory mask wearing is the right thing to do.
"However, for this measure to be fully effective it is important the Government extends this mandate to all public indoor and closed settings.
"This includes the hospitality industry – such as for staff in restaurants – where the public tend to spend long periods of time in close contact with others. We only have a small window of opportunity to get this right to ensure that we don't lose control of this new variant, which has the potential to have a devastating impact on the health service.
"The Government must act now, or we risk seeing even more unnecessary deaths." Labour has called for working- from-home guidance to be revived and face coverings in more settings. Shadow Foreign Secretary Lisa Nandy said: "We said mask wearing in crowded spaces and flexible working from home where people can ought to be part of Plan A."
But Mr Javid insisted "we're nowhere near" triggering the move or reintroducing social distancing.
He added: "Those types of measures carry a heavy price economically [and] socially in terms of health outcomes such as impact on mental health."
Mr Javid also said: "I think people should continue with their plans as normal for Christmas. I think it's going to be a great Christmas."
Experts were last night racing to track down contacts of a third UK case of the new Covid mutation. The UK Health Security Agency said the person tested positive after travelling to the UK, with the case linked to being in southern Africa.
It added: "The individual is no longer in the UK, but [we are] carrying out targeted testing at locations where the positive case visited when they were likely to have been infectious.
"While in the UK, the individual was in Westminster." UKHSA chief executive Dr Jenny Harries warned it is "very likely" more Omicron cases will be discovered in the coming days.
Press Association Images)
Official figures yesterday showed 37,681 new Covid cases and 51 more deaths. Anyone who has come into contact with a suspected case of Omicron must isolate for 10 days.
And everyone arriving in the UK from 4am tomorrow must have a "gold standard" PCR test and self-isolate until they provide a negative result.
More nations have identified Omicron infections. As of last night, 13 had been found in the Netherlands.
Denmark, Australia, Germany, Italy, Botswana, Israel and Hong Kong have also recorded cases.
Ten African nations have been placed on the UK's "red list" for travel.
It means that arrivals must quarantine for 11 nights in a Government-approved hotel. Labour MP Yvette Cooper has urged the Government to reinstate pre-travel tests because the new approach "leaves far too many gaps" – with potentially infected passengers able to travel home on public transport.
Dr Paul Burton, chief medical officer of drugs company Moderna, is "optimistic" about tackling the new strain which he said "looks dangerous".
Dr Angelique Coetzee, the South African doctor who discovered the variant, said the UK is "panicking unnecessarily", but added "maybe we will say something different" in two weeks.
She added: "What we are seeing in South Africa, and remember I'm at the epicentre, it's extremely mild." Government advisers here are this week expected to issue guidance on widening the booster programme.
Clive Dix, the former head of the Government's vaccine taskforce, has said that in April when he left the role he produced a plan "on what we should put in place right now to prepare for vaccine-resistant strains", but that ministers have ignored it.
Fight to save Christmas with tougher rules as more cases of 'worst Covid' Omicron hit UK have 864 words, post on www.mirror.co.uk at November 28, 2021. This is cached page on Europe Breaking News. If you want remove this page, please contact us.