The UK is to close all travel corridors from Monday to “protect against the risk of as yet unidentified new strains” of Covid, the PM has said.
Anyone flying into the country from overseas will have to show proof of a negative Covid test before setting off.
It comes as a ban on travellers from South America and Portugal came into force on Friday over concerns about a new variant identified in Brazil.
Boris Johnson said the new rules would be in place until at least 15 February.
It comes as a further 1,280 people with coronavirus died in the UK within 28 days of a positive test, taking the total to 87,291.
The latest government figures on Friday also showed another 55,761 new cases had been reported, up from 48,682 the previous day.
Meanwhile, more than two million people around the world have now died with the virus since the pandemic began, according to figures from Johns Hopkins University.
Speaking at a Downing Street press conference, the prime minister said it was “vital” to take extra measures now “when day-by-day we are making such strides in protecting the population”.
“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.”
People coming to the UK will need to quarantine for up to 10 days, unless they test negative after five days, in line with the current policy.
Mr Johnson added that the government would be stepping up enforcement at the border.
Travel corridors were introduced in the summer to allow people travelling from some countries with low numbers of Covid cases to come to the UK without having to quarantine on arrival.
Trade body Airlines UK said it supported the latest restrictions “on the assumption” that the government would remove them “when it is safe to do so”.
Tim Alderslade, its chief executive, said: “Travel corridors were a lifeline for the industry last summer and the government were right to bring them in when they did.
“But things change and there’s no doubting this is a serious health emergency.”
Speaking about the announcement, Clive Wratten, CEO of the Business Travel Association, said: “The BTA recognises that public safety must come first. With all travel corridors closed from Monday, it is imperative that the Government issues detailed information on where essential travellers can get acceptable tests to meet the UK’s entry requirements.
There are many essential workers who need to travel – medical researchers, energy suppliers and humanitarians to name a few. They must be able to undertake their vital work with confidence in procedures, and safe in the knowledge they can return home.”
Adding their thoughts to the announcement, UKinbound CEO Joss Croft, said “Consumer safety is paramount and although the removal of all travel corridors is regrettable, given the current trajectory of the virus it’s an understandable decision. With our borders effectively closed, the Government needs to provide urgent, tailored support for the inbound tourism industry. It simply cannot afford to continue excluding it from support channels, given its propensity to aid the UK’s economic recovery when we can travel again.
“To save the summer season, it’s also imperative that Government signals that these new measures are only temporary, and that the Government consults with industry to put in place a clear roadmap to reopen the sector, when it’s safe to do so.”