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, while parliament will be recalled to sit on Wednesday amid calls for a third national lockdown in England.
Live COVID updates as PM to address the nation
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.
Labour leader Sir Keir Starmer on Sunday demanded a national lockdown in England within 24 hours.
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".
On Sunday, the UK recorded more than 50,000 new coronavirus cases for the sixth day in a row - as the total number of COVID-19 deaths passed 75,000.
