People who test positive for coronavirus or show symptoms in the UK must now self-isolate for 10 days.
The change, announced by the UK’s four chief medical officers, comes as ministers try to avoid a resurgence of the virus.
Until now, those showing key symptoms – a new continuous cough, a temperature or loss of taste or smell – have had to self-isolate for at least a week.
The new advice is in line with World Health Organization guidance.
It comes after the prime minister warned of signs of a “second wave” of the pandemic in parts of Europe.
Speaking on BBC Breakfast before the announcement, Health Secretary Matt Hancock said the government wanted to “take a precautionary approach” and “protect people from that wave reaching our shores”.
- What’s the evidence Europe is having a ‘second wave’?
- UK signs deal for 60 million virus vaccine doses
Meanwhile, the government is also expected on Thursday to review the restrictions in Leicester again, a month after the city was put into extended lockdown following a spike in cases.
The UK requirement for people who test positive to isolate for seven days was always on the low side – plenty of other countries require 10 days or even longer.
As coronavirus is new, there is a lack of certainty over how long someone remains infectious.
Research shows a person can be infectious two days before symptoms develop and carry on being infectious during the period they have symptoms. For most, that lasts no more than seven days.
Those who have symptoms longer are already advised to carry on self-isolating.
But the decision to insist everyone isolates for 10 days is likely to have been made for a number of reasons.
There is plenty of evidence that people continue to shed the virus after symptoms end – although the degree to which this represents a risk of passing on the infection to another person is not clear.
Another factor that may have played a role in the decision is that widespread testing is beginning to pick up people in the asymptomatic stage.
And, finally, it sends an important signal. By extending the length of isolation, it acts as a warning against complacency.
Prof Peter Openshaw, who is part of a body advising the government on respiratory viruses, told the BBC’s Today programme that most transmission takes place “at the time of symptoms developing, possibly for two days before”.
However, he said 10 days would be a “safer margin” because there have been “rare cases” in which people have been able to pass the virus on for up to nine days.
“We don’t really know that there’s very much transmission actually going on in those last couple of days, but I think in terms of trying to generally put pressure on the virus now… I can absolutely understand why the government might wish to introduce these changes,” he said.
Those returning to the UK from certain countries are also being asked to quarantine for 14 days – a move that has sparked complaints from travel firms.
Ministers are also looking for a way to reduce the current 14-day quarantine period for arrivals to the UK, meaning that quarantine and self-isolation time periods could be standardised at 10 days.
Mr Hancock told Today that the government is looking at using testing to reduce the length of the quarantine period – but there would be no imminent changes.
He did, however, say that new countries could be added to the quarantine list in the coming days.
On Wednesday evening the government held a meeting to discuss which other countries would be joining the list of those not exempt from the quarantine rule, after a spike in cases saw Spain added over the weekend.
A senior government source told the BBC that Luxembourg was likely to be added this week but that – for the moment – the numbers in Belgium would continue to be monitored.
On Wednesday, leading travel and airline industry figures called for coronavirus testing at airports in the UK but the source said that “any new system had to be workable and at the moment it isn’t”.
Mr Hancock told Breakfast that the “big scientific challenge” with testing arrivals at the border is that people “can incubate this disease for many days without displaying any symptoms, and that wouldn’t show up in a test”.
Officials said a further 83 people with coronavirus had died in the UK, taking the total number of deaths to 45,961.
It also reported another 763 confirmed cases, taking the total to 301,455.
What are the rules on self-isolating?
Self-isolating means staying at home and not leaving it.
Anyone who has either tested positive for coronavirus or shown symptoms should isolate themselves for 10 days, and those who show symptoms should arrange to get tested.
- a loss of, or change in, your normal sense of taste or smell
They should continue to self-isolate if they still feel unwell after that initial period.
Other members of their household should isolate for 14 days and not leave their homes.
If you test positive you will be contacted by contact tracers, who will establish who else you might have passed on the infection to.
Anybody they deem to be at risk will have to isolate themselves for 14 days from the point of contact.
- ASK MARTIN LEWIS: Answering your questions about travelling to Spain
- HOOKED: How has lockdown affected drinking habits?
Please include a contact number if you are willing to speak to a BBC journalist.