Travellers from Portugal will have to isolate when arriving in Scotland and Wales but not England, sparking confusion.
The nations made different decisions at the weekly point when their quarantine lists are normally updated.
The UK government generally says countries where the figure is higher than 20 per 100,000 are at risk of being added to the list.
Areas where anyone arriving in Scotland from must quarantine from 4am on Saturday:
- French Polynesia
Areas where anyone arriving in Scotland from must quarantine from 4am on Friday:
- Portugal – excluding the Azores and Madeira islands
- French Polynesia
- Greek islands of Mykonos, Zakynthos, Lesvos, Paros, Antiparos and Crete
Scotland earlier this week added Greece to its quarantine list.
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Transport Secretary Grant Shapps, who has responsibility for England only, tweeted the quarantine list is kept "under constant review" and he would not "hesitate to remove countries if needed".
But he added "there are no English additions or removals today", though reminded tourists that destinations exempt from quarantine "can and do change at very short notice".
Holidaymakers in Portugal were scrambling to get home this week.
British Airways flight prices jumped to more than £500 for Thursday, and EasyJet sold out all its flights from Faro to airports in Britain for Wednesday, Thursday and Friday.
It is understood ministers from the heads of all four UK nations are meeting this evening to discuss the situation.
Kelly Jones and her family changed their flights back from the Algarve from Saturday to Friday to ensure her children would not miss out on two weeks of school.
The 45-year-old said she paid Jet2 £900 on Monday to bring the trip home to Birmingham forward a day in anticipation of quarantine measures being reintroduced and hit out at the "absolutely disgusting" situation.
"The government just change the goalposts left, right and centre at the moment," she said. "It's embarrassing.
"They don't make things clear enough. They say they need the rate under 20 and it's gone above that this week, so why wouldn't you think it would go on the quarantine list tonight?
"You can guarantee if I hadn't have booked those flights on Monday, that air bridge would have been removed tonight."