Chief medical officers announce the new rule as the UK braces for winter amid warnings of a “second wave” brewing in Europe.
Self-isolation rules are being changed as scientists warn people with coronavirus may be infectious for longer than previously thought.
The chief medical officers of all four UK nations said anyone with symptoms or a positive test result should isolate for ten days instead of seven.
In a statement, the four scientists said evidence – while limited – “has strengthened” to show people with the virus “have a low but real possibility of infectiousness” for up to nine days after catching it.
Extending self-isolation will “help provide additional protection to others in the community”, they added – particularly vulnerable people who have been shielding since March.
It remains the case that people with coronavirus symptoms are most infectious just before or in the first few days after their symptoms begin.
Anyone with symptoms who has a negative test during their isolation period can be released from it.
Those who have come into close contact with someone who has tested positive for COVID-19 will still have to stay at home for the same amount of time as before – 14 days.
The UK has followed some other countries in extending the isolation period to 10 days.
But the World Health Organisation recommends isolating for ten days after onset, plus an additional three days once symptoms have subsided.
It comes as new figures showed England suffered the highest levels of excess deaths of any country in Europe over the first half of 2020.
Earlier, Health Secretary Matt Hancock said he was “worried” about another peak, telling Sky News’ Kay Burley@Breakfast there is a “second wave starting to roll across Europe”.
“It’s something I worry about and I worry about it because we can see it coming,” he said.