International arrivals will need to show a negative coronavirus test before travelling to the UK under a tightening of border restrictions.
All travellers, including British citizens, will have to take a test up to 72 hours before departing the country they are in. Airlines, ferry operators and cross-Channel rail services will have to check for proof of a negative result and bar passengers without one.
Anyone who lands in the UK from next week without a negative test result faces an on-the-spot £500 ($679) fine.
Transport Secretary Grant Shapps said the move adds "an extra layer of defence" and comes amid concern over the highly transmissible South African variant of the virus.
"There are concerns that the South African one in particular - about how effective the vaccine would be against it - so we simply cannot take chances," he told Sky News.
Ministers had been under pressure to close the UK border to non-citizens - as the US has done - but Mr Shapps said this was ineffective.
"We are an island. We require people and goods to function, to bring in the medicine and PPE," he said.
Heathrow Airport chief executive John Holland-Kaye said the negative Covid test result must only be a temporary requirement.
“We need to have a roadmap for how we get out of this because aviation is vital to us as a small island trading nation," he said.
He also said that vaccination programmes in Britain and other countries gave him hope for a travel recovery later this year.
“We’ll see flights starting to come back and passenger numbers building up through the summer and then into the autumn,” he said.
All travellers arriving from countries not on the safe travel list will still be required to self-isolate for 10 days, regardless of their test result.
However, travellers from the UAE will not need to follow strict quarantine restrictions when entering Britain, it was announced on Thursday night.
The move means that business travellers and thousands of holidaymakers from the UK enjoying the winter sun in Abu Dhabi and Dubai will still be able to fly to the UK without having to enter quarantine for 10 days.
As part of other measures to suppress Britain's increasingly high infection rate, some countries have been taken off the "travel corridor", including Israel and countries bordering South Africa, which has a highly infectious Covid strain.
The travel restrictions will now be extended to southern African countries and Israel from 4am on Saturday, January 9, to protect against the mutant strain.
Israel was removed from the travel list after “data showing a significant increase in confirmed cases", the Department of Transport said.
The country is experiencing a very high infection rate, at almost nine times the level it was a month ago, and is averaging 31 deaths a day.
Mauritius, the Seychelles and Botswana have also been removed from travel list.
“The government has responded swiftly to new evidence showing an urgent need to halt travel from all southern African countries to help prevent the spread of a new Covid-19 variant identified in South Africa,” the department said.
The measures will be in place for an initial period of two weeks while the UK reviews scientific data and other ways to protect Britain and its partners in Africa, it said.
Entry into England will be banned for those who have travelled from or through any southern African country in the past 10 days, including Namibia, Zimbabwe, Botswana, Eswatini, Zambia, Malawi, Lesotho, Mozambique and Angola.
British and Irish nationals who have travelled to those countries in the past 10 days will have to isolate themselves along with members of their household.
The move, in addition to the travel ban imposed on South Africa on December 23, follows new data on the steep rise of infections from the new variant.
“Urgent restrictions are therefore now needed to prevent the spread of this strain in the UK,” the department said.