Germany has designated the UK a "virus variant region", meaning anyone arriving from Britain and Northern Ireland will need to quarantine for two weeks on arrival.
It comes a week after Germany declared the UK a COVID "risk area".
According to guidance from German authorities, a virus variant region is "at particularly high risk of infection due to widespread occurrence of SARS-CoV-2 virus variants of concern".
Great Britain, Northern Ireland, all British Overseas Territories, the Isle of Man and the Channel Islands are all covered by the new restrictions, which take effect from midnight on Sunday.
Germany is on the UK’s amber travel list – meaning people should not go on holiday there, and anyone arriving back in Britain will need to quarantine for 10 days or go through a test-to-release scheme.
Speaking about the latest quarantine rules, a German government source told Reuters news agency: "We want to play it safe.
"In this important phase of the vaccination campaign, the entry of problematic mutations must be avoided as far as possible."
According to Johns Hopkins University, Germany has administered 43,730,162 vaccine doses – with 10,915,832 people fully inoculated.
This means 13.13% of the population have had both shots.
In the UK, 37,518,614 first doses have been given out, while 21,659,783 second doses have been administered – equivalent to 32.43% of the population.
Earlier, Germany’s chancellor Angela Merkel urged people to be more responsible as restrictions in the country began to ease on Friday.
Cases numbers are starting to decline in a country which has seen 3,638,504 people test positive and 87,135 COVID deaths.
Most of Germany’s 400 cities and counties have fallen below the bar of 100 cases per 100,000 people needed to start easing measures.
Chancellor Merkel said: "We can be glad that (infection rates) have declined so far in recent days and in the last two weeks that we can think about opening steps.
"I hope that, after the long time with closures and opportunities they didn’t have, that people will treat these opportunities very responsibly."
She added: "The virus has not disappeared."
Beer gardens, cafes and restaurants in Berlin have started serving customers outdoors for the first time in months – as long as they present a negative COVID test or a vaccination certificate.