The UK has reported a further 1,041 people have died with coronavirus, the highest daily death toll since April.
It came as 62,322 new cases were recorded, the highest daily rise since mass testing began, as MPs debated England's new curbs.
Health Secretary Matt Hancock said doctors could be forced to ration treatment without the new lockdown.
There are 30,074 Covid patients in UK hospitals, he said, as an ambulance trust told of severe pressure.
The number of those who died within 28 days of a positive test in the past week is 37% higher than the previous seven days.
Mr Hancock told MPs the consequences of inaction could be similar to scenes elsewhere in the world - of overrun hospitals and doctors choosing "who to treat and who to turn away".
"If we don't act now, we know that eventually the NHS would not be able to cope," Mr Hancock said.
"We know that while the winter weeks will be difficult, we now know what the way out looks like," he added, referencing the accelerated roll out of vaccines.
West Midlands Ambulance Service experienced its busiest-ever day on Monday, handling 5,383 emergency calls due to a combination of Covid-19 pressures and winter weather.
All of the UK is now under strict virus curbs, with Wales, Northern Ireland and most of Scotland also in lockdown.
While England's lockdown became law at midnight, MPs will vote this evening on the restrictions after Parliament was recalled.
Meanwhile, GCSEs, A-level and AS-level exams will be cancelled this year in England, replaced by a form of teacher-assessed grades, Education Secretary Gavin Williamson said.
"This year, we're going to put our trust in teachers, rather than algorithms," he said, following controversy over
the way exam grades were awarded to some students last year.
All national curriculum tests for primary school children, often known as Sats, are also cancelled, Mr Williamson confirmed.
He said that during this lockdown, every school will be expected to provide between three and five hours of virtual teaching each day and that 750,000 laptop and tablet devices will have been distributed by the end of next week.
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