All travellers to England and Scotland from international destinations will from next week need a test negative for Covid before they can enter the country.
Failure to comply with the new regulations will lead to an immediate £500 fine.
Under plans set out by the Transport Secretary, passengers arriving by boat, train or plane will have to take a test up to 72 hours before leaving the country of departure.
Grant Shapps, announcing the move on Friday, said it was designed to prevent new variants of the disease emerging in countries like South Africa and Denmark.
There will be a limited number of exemptions, including hauliers, children under 11, crews and for those travelling from countries without the infrastructure available to deliver tests.
Arrivals from the Common Travel Area with Ireland will also be exempt.
While the announcement only covers England and Scotland, ministers were said to be working closely with the devolved administrations on similar measures.
The move follows the decision to suspend all direct travel from South Africa following the emergence there of a new strain of coronavirus.
This variant is thought potentially to be even more virulent than the mutant variant which has led cases to surge in the UK.
Mr Shapps said: “We already have significant measures in place to prevent imported cases of Covid-19, but with new strains of the virus developing internationally, we must take further precautions.
“Taken together with the existing mandatory self-isolation period for passengers returning from high-risk countries, pre-departure tests will provide a further line of defence – helping us control the virus as we roll out the vaccine at pace over the coming weeks.”
The announcement comes at a time when the latest lockdown restrictions across the four nations of the UK mean there is very little international travel.