Prime Minister Boris Johnson is set to make an announcement to the nation tonight.
It will be a pre-recorded statement to provide an update on booster vaccines, Downing Street has said.
The announcement comes as the UK Covid Alert Level has been increased from Level 3 to Level 4 "in light of the rapid increase in Omicron cases", the four UK chief medical officers said in a joint statement.
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But is also just as Johnson faces mounting pressure from the number of stories and allegations about several parties taking place over the festive period last year while the UK was under a series of tight lockdown laws.
A No10 spokesperson said: "The Prime Minister will give an address to the nation from Downing Street this evening, providing an update on the booster programme. This will be broadcast at 8pm."
Coronavirus booster vaccines are to be made available to people aged 30-39 in Scotland from Monday and to 18-29-year-olds from later in the week, Health Secretary Humza Yousaf has said.
It follows a decision by the UK Government to make the jabs available to those in the 30-39 age range in England.
Writing on Twitter, Mr Yousaf said: "From tomorrow (Mon 13th) you can book your Booster if you're aged 30-39.
"We intend on opening portal to 18-29yr olds later in the week, details to follow.
"We know just how important a tool vaccination, and in particular the Booster is in our fight against the virus."
He added: "A reminder, to be eligible 12 weeks must have elapsed between your 2nd dose and Booster.
The Government said, as of 9am on Sunday, there had been a further 48,854 lab-confirmed Covid-19 cases in the UK.
It also said a further 52 people had died within 28 days of testing positive for Covid-19.
Separate figures published by the Office for National Statistics show there have now been 171,000 deaths registered in the UK where Covid-19 was mentioned on the death certificate.
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