Every single UK travel corridor will be closed from 4am on Monday, Boris Johnson has announced.
Travellers from all countries must offer proof of a negative Covid-19 test taken in the previous 72 hours before departing for the UK.
International arrivals must then quarantine for 10 days, although they have the choice of doing an extra test on day five to shorten the isolation period.
The decision comes after a number of new strains were detected inside the country – including one that started in Brazil and another that was found in South Africa.
The Prime Minister told a Downing Street press conference today: ‘It’s precisely because we have the hope of that vaccine and the risk of new strains coming from overseas that we must take additional steps now to stop those strains from entering the country.
‘Yesterday we announced that we’re banning flights from South America and Portugal and to protect us against the risk from as-yet-unidentified strains we will also temporarily close all travel corridors from 0400 on Monday.
‘Following conversations with the devolved administrations we will act together so this applies across the whole of the UK.’
Almost 45% of the over-80s and almost 40% of care home residents have now been vaccinated, Mr Johnson said.
However, it is ‘not the time for relaxation’ as complacency will have ‘fatal’ consequences, he has warned.
There are now more than 37,000 Covid patients in hospital amid the third national lockdown.