Britons returning home after overseas holidays are facing a scramble to beat changing quarantine rules and soaring air fares.
Travellers coming from Croatia and Austria to the UK must land before 4am on Saturday or face having to self-isolate for two weeks.
Anyone returning to the UK from Trinidad and Tobago will also have to quarantine for 14 days after cases on the Caribbean island more than doubled in a week.
Transport secretary Grant Shapps also announced travellers returning from Portugal to the UK from 4am on Saturday will no longer have to self-isolate for two weeks.
Ministers have faced criticism for their handling of quarantine rules, with Gatwick Airport calling for the flexibility to remove restrictions from certain locations within nations.
Such a policy, a spokesperson said, "would also reflect the UK government's domestic approach to containing outbreaks by implementing local lockdowns" and "help the aviation industry to recover and protect jobs."
The threat to those jobs was illustrated by July's passenger total of 280,000, compared to 4.7 million in 2019.
As holidaymakers scramble to get back to the UK in time to avoid quarantine, they are facing rises in air fares from nations added to the quarantine list.
British Airways was advertising tickets for an economy class flight from Zagreb, Croatia to London early on Friday at €308 (£276), compared to €92 (£82) on Monday and €96 (£86) on Thursday.
Similarly, the airline was on Thursday night advertising an economy seat on a flight from Vienna to London Heathrow for €538 (£482). The price for a flight on Sunday was €122 (£109).
The Scottish justice minister has announced that Switzerland has also been added to Scotland's quarantine list - this does not apply for people returning to the rest of the UK.
The UK Foreign Office has said it would look at putting any country with more than 20 cases per 100,000 people on its quarantine list.
Croatia's average number of cases has risen to 29.5 cases per 100,000 people in the past week - compared to a rate of 13.54 per 100,000 a week ago.
The mayor of Dubrovnik, one of Croatia's most popular tourist cities, said he had tried to speak to the British government to exclude travellers to the city from quarantine - as Germany has done - because he said it has had very few cases.
Mato Frankovic said he had hoped airport testing for coronavirus would be introduced in the UK instead of quarantine.
He told Sky News: "But we were not successful.
"I do hope those British citizens who want to come to Dubrovnik still do, and I want to send a very strong message that Dubrovnik is a COVID-safe town."
He said people immediately started cancelling hotel rooms when the quarantine was announced and for a city where Britons are the number one visitors, the decision will be devastating.
Trinidad and Tobago's cases have risen rapidly in the past week, with 25.81 cases per 100,000 people in the past week compared to 9.10 cases per 100,000 the previous week.
Austria's rate has nearly doubled in the past week, with 20.31 cases per 100,000 in the past seven days, up from 10.45 cases per 100,000 the week before.
A Department for Transport (DfT) statement said: "The government has made consistently clear it will take decisive action if necessary to contain the virus, which includes removing countries from the travel corridors list rapidly, if the public health risk of people returning from a particular country without self-isolating becomes too high."
People currently in Croatia, Trinidad and Tobago and Austria have been encouraged to follow local rules and check the Foreign Office's travel advice for more information.
"The government is urging employers to be understanding of those returning from these destinations who now will need to self-isolate," the DfT added.
Portugal's government and tourist industry expressed anger when the country was placed on the quarantine list when it was created at the beginning of July.
The country's number of cases dropped in the past week to 14.38 cases per 100,000 people, compared to 15 per 100,000 the week before - and has not been over 20 per 100,000 since the week of 15-22 July.
In many other parts of Europe there has been an increase in cases:
The UK had 1,182 new cases on Thursday
Italy recorded 845 new cases on Thursday, the highest daily increase since lockdown was eased
France had 4,771 cases on Thursday, compared to 3,776 on Wednesday
Spain reported 3,349 cases on Thursday - more than 1,000 in Madrid
Germany recorded 1,707 cases on Thursday - the largest daily increase since 26 April.