Health Secretary Matt Hancock will lead a Downing Street press conference tonight.
No 10 made the announcement amid changing travel rules and further rollout of the coronavirus vaccine.
Downing Street has not confirmed what time the Health Secretary will be addressing the nation.
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Coronavirus vaccines will be offered to millions of over 70s and the clinically extremely vulnerable from this week as the Government expands the rollout amid a border crackdown to keep out new strains.
More than 3.8 million people in the UK - including over-80s, care home residents, and NHS and social care staff - have already received their first dose of a Covid-19 vaccine, but from Monday it will be rolled out to the next two priority groups.
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The Government said it would remain the priority to vaccinate those in the first two groups, but that sites which have enough supply and capacity to vaccinate more people will be allowed to offer jabs to the next cohorts.
Boris Johnson has pledged to offer vaccinations to the first four priority groups by the middle of next month, while Dominic Raab said on Sunday that all adults would be offered a first dose by September.
The expanded rollout arrives as a ban on quarantine-free travel into the UK came into force at 4am in a bid to keep out new coronavirus strains - such as those which have been discovered in Brazil and South Africa.
The new rules mean arrivals from every destination will need to self-isolate for 10 days, or receive a negative result from a coronavirus test taken at least five days after they enter the UK.
