People entering England and Scotland will have to show a negative COVID-19 test result starting next week as authorities try to ramp up protection against new, more infectious strains of the coronavirus from other countries.
Passengers arriving by boat, plane or train will have to take a test a maximum of 72 hours before departure, mirroring measures taken last year by other countries around the world.
"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," Transport Secretary Grant Shapps said.
He said there were concerns that vaccines might not work properly against the highly transmissible variant of the coronavirus discovered in South Africa, echoing recent comments from other government officials.
On Thursday, Britain said it would extend a ban on travellers entering England from South Africa to include other southern African countries, and non-essential travel in and out of the United Kingdom is restricted.
Prime Minister Boris Johnson ordered a new lockdown for England this week after a surge in cases linked to another variant of the virus believed to have originated in the country.
Scotland, which like the rest of the United Kingdom has tight COVID-19 restrictions in place, said it too would require travellers to show negative tests and the rule is also expected to be applied by Wales and Northern Ireland.