From today (Mon 14 Dec), the self-isolation period for contacts of people with coronavirus has been shortened from 14 days to 10 in the UK.
The change also applies to anyone returning from high risk countries.
Wales already announced a shortening of the self-isolation period, but from today, the rule will apply to all four nations across the UK.
It means that anyone who has been self isolating for 10 days or longer can now end their quarantine.
A 10 day long quarantine rule already applied to people who had symptoms or a positive test.
Most infectious when symptoms first develop
It's understood that the change has been made as it reflects the highest risk period, when people are most likely to pass the virus on.
Scientists now know that people are most infectious to others around the time they first develop symptoms. By day 10, only around two per cent will be infectious.
Experts now believe, therefore, that a 10 day period of isolation is sufficient to avoid passing on the virus.
'Self-isolation is still essential'
The UK's four chief medical officers said in a statement, "After reviewing the evidence, we are now confident that we can reduce the number of days that contacts self-isolate from 14 days to 10.
"People who return from countries which are not on the travel corridor list should also self-isolate for 10 days instead of 14 days."
They added that self-isolation was "essential to reducing the spread of Covid as it breaks the chains of transmission."
Though the rule comes into force today, it's believed that the NHS app in England won't update its 14 day isolation counter until Thursday 17 December.
If your timer hits three days between Monday and Thursday, therefore, you can leave isolation.
Currently, a pilot in Liverpool is looking to reduce the numbers of people self-isolating even further by testing the contacts of positive cases every day for a period after exposure and only asking them to isolate if they test positive. This could be particularly helpful for schools, as it will prevent large numbers of teachers and children having to self-isolate.
Provided the pilot is a success, it's thought this system would be rolled out in 2021.