The new mutant coronavirus strain is now ripping through areas outside of England's south east, the government's top medical advisor has warned.
Professor Chris Whitty told the Downing Street press conference that the fastest increase of the new variant remains in the east of England, London and south-east.
But it is "now taking off in other areas as well," he said.
England's chief medical officer said there were some indications the virulent new strain's impact levelling off, following a period of Tier 4 restrictions in hotspots and as the country enters a third national lockdown.
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However he added hospitalisations across England are "rising very rapidly and, of course, we are still in the middle of winter".
Prof Whitty also warned there would 'inevitably' be an increase in deaths in January.
He added that one in 50 people being estimated to have coronavirus across the UK in the days following Christmas is "really quite a large number indeed".
He cited the Office for National Statistic estimates, as he said that the second lockdown in November had brought down rates.
But he warned the risks will not disappear in the spring, despite the vaccine rollout.
In a stark warning, Prof Whitty said the UK could still face restrictions anew next winter.
"If people don't take the 'stay at home' seriously, the risk at this point in time, in the middle of winter with this new variant, is extraordinarily high," he said.
"We shouldn't kid ourselves (that) this just disappears with spring."
He said the new variant and the worst period of winter pressures on the NHS had combined to lead to current surging rates of the virus.
The UK today recorded 60,916 new cases of Covid-19 in the last 24 - in the largest daily increase reported so far.
And a further 830 people died within 28 days of testing positive for the virus as of Tuesday.
Boris Johnson told the news conference tonight that in the days leading up to the lockdown announcement the Government had been looking at the new variant of coronavirus.
The Prime Minister said officials had become aware of its rapid spread on December 18.
Mr Johnson said it had been hoped that Tier 4 measures would have had an impact and allow for schools to be kept open.
However he had been forced to take action in plunging England into a third national lockdown last night, he added.
Highlighting recent infection figures, he continued: "It was clear that we got to a situation where Tier 4 on its own couldn't be relied upon to get the virus under control and that's without really going the whole way and asking people to stay at home and, sadly, to close schools as well.
"That's why we took the step that we did."
