The UK is ready to bring back quarantine 'very rapidly' if needed for people returning from countries like France, Downing Street has warned.
The Prime Minister's official spokesman suggested any decision to change the rules might not wait until a weekly review, which is usually held on or around Thursday.
No10 warned "during this pandemic there isn’t a risk free way of travelling overseas", and said: "If we feel that we need to act in relation to the travel exemptions risk then we’ll do so."
It comes after a rise in Covid-19 cases in France, with face masks being made mandatory in busy parts of Paris as of Monday.
That has fuelled speculation that 14-day quarantine will be imposed on people arriving in the UK from France - including Brits returning from holiday.
Asked if the rules were set to change for France later this week, the PM's spokesman said today: "We keep the data for all countries and territories under constant review.
“Any decision to update the exemptions list will be informed by the latest health data.
“And we can and will act rapidly if we judge the public health risks of not requiring travellers to self-isolate increase beyond an acceptable level.
“We have been updating the exemptions list on a weekly basis in order to make sure it reflects the changes in the international health picture.”
Asked if any decision would be made on a Thursday, the spokesman replied: “If there is a need to act very rapidly in order to protect public health then we wouldn’t hesitate to do so.”
He went on: “I’m not referencing any particular country here and I think it’s important that I stress it.
“But it is the case that we can and will act rapidly if that is necessary.”
The spokesman said countries' statuses are kept under a “constant review", looking not just at the infection rate per 100,000 people, but also at the testing rate and reliability of data which each country produces.
Boris Johnson earlier said ministers will "not hesitate" to impose a quarantine system for travellers from other countries to the UK if needed.
The Prime Minister, speaking on a visit to St Joseph's school in Upminster, urged those who go abroad to look at the Foreign Office travel advice carefully.
Mr Johnson said: "I don't want to advise people about their individual holidays, individual decisions, they should look at the travel advice from the Foreign Office clearly.
"But what I will say, and I hope people would expect us to do this, in the context of a global pandemic, we've got to keep looking at the data in all the countries to which British people want to travel.
"Where it is necessary to impose restrictions or to impose a quarantine system, we will not hesitate to do so.
"It's been a huge effort for the entire population of this country to get the disease down to the levels that we are currently seeing, but we do not want reinfection and that's why we've got to keep a very, very close eye on the data in destinations around the world."
Last month, the UK Government announced that travellers to the UK from Spain would have to quarantine for 14 days on their return to the country.
Luxembourg, Andorra, The Bahamas and Belgium were also added to the UK's 14-day quarantine list last week.
