All travel corridors to the UK will be closed from 4am Monday (18 January), meaning any passengers travelling to the country must obtain a negative COVID test 72 hours before departure.
Arrivals will be asked to show proof of the negative test and their passenger locator form and could face fines of £500 if they refuse to comply. Once in the country, arrivals must quarantine for 10 days or take another test on day 5 and wait for proof of another negative result.
Following conversations between Downing Street and the devolved administrations, these rules apply across the whole of the UK.
The move, which follows the UK's ban on flights from South America and Portugal yesterday, is to protect against new and 'as yet unidentified new strains' of the virus, the prime minister said today.
Boris Johnson also warned the government 'will be stepping up our enforcement both at the border and in-country'.
Mr Johnson told the nation that since yesterday there had been 55,761 positive cases and 1,280 recorded deaths, stating: 'This is not the time for the slightest relaxation of our national resolve and individual efforts.'
He said: 'It is precisely because we have the hope of the 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 were banning flights from South America and Portugal and to protect us from as yet unidentified new strains we will also temporarily close all travel corridors from 4am Monday.
'This means if you are coming to this country you must have proof of a negative COVID test that you have taken in the 72 hours before leaving and you must have filled in your passenger locator form and your airline will ask for proof of both before you take off.'