All international passengers will soon have to test negative for Covid-19 before travelling to the UK.
People arriving by plane, train or boat, including UK nationals, will have to take a test up to 72 hours before leaving the country they are in.
Transport Secretary Grant Shapps said travellers “can’t board… without having that negative test”.
It will be on top of the rule to self-isolate for 10 days when arriving in the UK.
Mr Shapps said the government was “very keen to do it now” because of the new South African variant of the virus, which he said was “causing great concern with the scientists”.
“They’re not sure whether for example the vaccine will be able to deal with it in the first place, and we’re very, very keen to keep it out,” he told BBC Breakfast.
The new measures are expected to come into force across the UK next week, and “as soon as possible” in Scotland.