The UK is to close all travel corridors from Monday to protect against unidentified Covid strains.
Speaking from Downing Street, Prime Minister Boris Johnson declared all arrivals to the UK must have proof of a negative test in the previous 72 hours and then immediately go into a 10-day isolation period, until they test negative after five days.
The border controls come almost a year since Britain first went into lockdown.
Criticism was again aimed at Mr Johnson and his government for again acting too slowly.
"What we're doing now is taking steps as you'd expect to protect ourselves against the new variant," he said.
"What we can't have is a new variant with unknown qualities coming in from abroad - that's why we've set up this new system."
While 3.2 million people have been vaccinated so far in the UK, the Covid death toll is now at 87,295 after a further 1,280 deaths since yesterday.