Boris Johnson will make a TV address tonight to set out “further steps” to combat the spread of COVID-19.
The prime minister is expected to speak at 8pm amid calls for a third national lockdown in England.
Government sources said the UK’s coronavirus alert level will be raised from 4 to 5 for the first time, which would mean there is judged to be a “material risk of healthcare services being overwhelmed”.
It has also been announced the House of Commons will be recalled from its current recess to sit on Wednesday, so MPs can hear from Mr Johnson and to debate coronavirus restrictions.
A Number 10 spokesman said: “The spread of the new variant of COVID-19 has led to rapidly escalating case numbers across the country.
“The prime minister is clear that further steps must now be taken to arrest this rise and to protect the NHS and save lives.
“He will set those out this evening.”
Earlier on Monday, Mr Johnson had warned there was “no question we will have to take tougher measures” and vowed the government would “do everything we can to keep the virus under control”.
On a visit to a vaccination centre as the national rollout of the Oxford/AstraZeneca vaccine got under way, the prime minister said there were “tough, tough” weeks ahead in the UK’s fight against COVID-19.
He spoke shortly before First Minister Nicola Sturgeon announced a nationwide lockdown will be introduced in Scotland from midnight tonight.
Northern Ireland First Minister Arlene Foster – who imposed a six-week lockdown in Northern Ireland from Boxing Day – revealed she and the other devolved administrations were due to speak to the UK government at 5pm “regarding a coronavirus response across the four nations”.
The closure of schools would be “part of the discussions”, Ms Foster said.
Labour leader Sir Keir Starmer on Sunday demanded a national lockdown in England within 24 hours.
In an interview with Sky News on Monday, Sir Keir said it was “inevitable” that all schools would have to close.
“We need a national set of restrictions, it is inevitable that closing schools is going to have to be part of that,” he said.
“As soon as possible we need the national plan in place and, if that can be done today or tomorrow, we will support the prime minister in that.”
Former health secretary Jeremy Hunt, who was beaten to the Conservative leadership by Mr Johnson in 2019, has also called for action “right away” in a bid to ease “off-the-scale” pressures on hospitals.
Mr Hunt, now the chair of the House of Commons health committee, wants all schools to be closed, international travel to be stopped, and all household mixing to be banned.
“In the face of exponential growth even waiting an extra day causes many avoidable deaths,” he said.
Liberal Democrat leader Sir Ed Davey and London mayor Sadiq Khan are also among those to have called for a third lockdown in England.
Health Secretary Matt Hancock did not rule out a new national lockdown for England during a Sky News interview on Monday.
He warned the new coronavirus variant was “much easier to catch”, with the effect now being seen in “lots of different parts of the country”.
New polling published by YouGov suggested 79% of Britons are supportive of another lockdown for the UK, compared to 16% who are against a fresh nationwide shutdown.
The UK recorded 58,784 new coronavirus cases on Monday – the highest daily total since the start of the pandemic.
It is the seventh day in a row that there have been more than 50,000 daily cases.
Government figures also showed there have been 407 more deaths in the past 24 hours.
In a note sent to MPs, Speaker Sir Lindsay Hoyle revealed the House of Commons will sit from 11.30am on Wednesday in order to hear a statement from Mr Johnson and to debate public health regulations.
“As per my advice on the previous recall, I would strongly urge you NOT to physically come to Westminster to participate in any business unless absolutely necessary due to the current severe public health situation,” Sir Lindsay said.