Britons have been told not to hug and kiss relatives over Christmas as Prime Minister Boris Johnson on Thursday raised the spectre of a January lockdown.
Speaking at a Downing Street news conference announcing Britain's tiered social restriction measures, Chris Whitty, England's chief medical officer warned: "The fact you can do something doesn't mean you should."
The government has allowed up to three households to be able to mix between December 23 and 27 to cover the Christmas period, while urging people to err on the side of caution.
But Prof Whitty said that people may be asymptomatic and may accidentally transfer the virus to elderly relatives by hugging and kissing them.
His warning comes as the government faces a rebellion over the tier system from Tory MPs who say the approach is unfair.
Housing Secretary Robert Jenrick said he wasn't surprised there was anger on his own side.
He told Sky News: "The task is to persuade our parliamentary colleagues."
Speaking in the same briefing on Thursday, Mr Johnson warned of a "hard winter" ahead before vaccines begin to make a significant difference.
"I really wish it were otherwise but if we're going to keep schools open as we must, then our options in bearing down on the disease are necessarily limited," he said.
His government has been looking to strike a balance between containing the virus and allowing people their freedoms.
However, Mr Johnson warned that a second strict national lockdown may follow in the New Year if people do not adhere to the new rules.
Mr Johnson admitted the tougher tiers would "bring a great deal of heartache and frustration" and admitted that pubs and restaurants had borne the brunt of the shutdown.
But the Prime Minister said he was "convinced" that in a few months the nation would have a vaccine and "by April things will genuinely be much, much better."
The news comes as tens of millions of Britons have found out they face the toughest coronavirus restrictions after England's national lockdown ends on December 2.
About 99 per cent of England's population was placed in the toughest two tiers.
Much of the north and Midlands were placed in the harshest Tier 3 restrictions - a hammer blow to the hospitality industry which will be forced to shut in those areas.
Announcing the tiers, Health Secretary Matt Hancock told MPs: "Hope is on the horizon but we still have further to go so we must all dig deep, the end is in sight, we mustn't give up now.
"We must follow these new rules and make sure that our actions today will save lives in future and help get our country through this."
London and Liverpool avoided the harshest restrictions by being placed in Tier 2 – allowing hospitality venues to open but preventing indoor household gatherings.
But while there is some relief in London and Liverpool, there is misery in Manchester.
The city, which refused to be placed in the toughest tier before lockdown, will now be forced into Tier 3.
Birmingham, Newcastle, Leeds, Hull, Wolverhampton, Blackpool and Kent were also placed in the highest tier.
Only Cornwall, the Isle of Scilly and the Isle of Wight are in Tier 1, or medium alert.
Tier 3 – representing very high alert – prevents restaurants and pubs from opening and a travel warning advises people against entering or leaving the area.
Mr Johnson said the new system would be reviewed every two weeks.
Tier allocations will be reviewed for the first time by December 16, which the government said allows for "the possibility of areas which continue to make progress in slowing the spread of the disease" to be moved down a tier before Christmas.
Allocations will be based on health advice, including pressure on the NHS, case detection rate, how quickly cases are rising or falling, and local outbreaks.
Tier 3 areas will be eligible for army support to carry out rapid testing using “lateral flow” devices that give results in less than an hour.
The highest level of restrictions could be catastrophic for the hospitality industry, with bars, cafes and restaurants forced to close except for those offering takeaway services.
Fullers, one of England’s biggest pub chains, announced a £22 million ($29.4m) loss before tax in the six months ended September 26.
Chief executive Simon Emeny said it was unjustified for the hospitality sector to be targeted by the new tier system.
He told BBC Radio 4's Today programme: "The difficult pill for us to swallow is the extra restrictions in Tier 2 will render 73 per cent of sites unprofitable and unable to open.
“The attitude towards the hospitality sector seems to have turned on its head in the last month.”
However, Liverpool mayor Joe Anderson, whose brother died from coronavirus, said Tier 3 restrictions were effective in reducing infection rates.
The city was placed in the toughest tier before lockdown and piloted a mass testing programme.
“It’s about saving lives,” he said. “There is no question the action we took in Liverpool saved lives. We’ve been able to bring the virus back under control again.”