A number of European countries have banned, or are planning to ban, travel from the UK to prevent the spread of a more infectious coronavirus variant.
The Netherlands and Belgium have halted flights, with Italy to follow suit. Trains to Belgium are also suspended.
Ireland is expected to restrict flights and ferries from midnight (23:00 GMT) on Sunday. France and Germany are among others considering similar action.
The new variant has spread quickly in London and south-east England.
Prime Minister Boris Johnson on Saturday introduced a new tier four level of restrictions, scrapping a planned relaxation of rules over the Christmas period for millions of people.
Top health officials said that there was no evidence the new variant was more deadly, or would react differently to vaccines, but it was proving to be up to 70% more transmissible.
What is the new variant?
In the UK, it was first identified in the middle of October from a sample taken in September.
The World Health Organization (WHO) says the same mutation has also been detected in the Netherlands, Denmark and Australia.
Dr Catherine Smallwood, of WHO Europe, said that as of 20 December, the numbers in those countries were small, nine in Denmark and one each in the other two nations. But she said other countries had notified WHO of other variants “that also carry some of the genetic changes seen in the UK variant”.
The initial coronavirus has a lower “viral load”, which makes it slower to be passed on
The new UK variant has been shown to spread faster than the original virus – up to 70% more transmissible based on modelling figures – but scientific details on the genetic changes, and how they could affect the behaviour of Covid-19, remain unclear.
Although there is no indication the variant will be more resistant to already-developed vaccines, the mutation does involve the spike protein of the virus.
This is the part that helps it infect cells – and also the part the vaccines have been designed to target. So although scientific experts have warned against an alarmist response, they also say it is essential to track the variant and try to stay ahead of the virus.