Portugal, Spain, Malta and Hong Kong have announced new restrictions on UK tourists amid growing concern over the Delta variant.
The Portuguese government imposed a mandatory 14-day quarantine requirement on arrivals from the UK who are not fully vaccinated.
This puts UK holidaymakers in the same risk category as those from South Africa, Brazil, India and Nepal.
Previously, UK visitors were exempt from quarantine if they had evidence of a recent negative coronavirus test.
The new rule, which came into effect on Monday, does not apply to Madeira.
The island will be added to the UK Government’s green travel list on Wednesday, meaning UK holidaymakers visiting the island will no longer need to self-isolate on their return.
Mainland Portugal will remain on the amber list.
People arriving in the UK from locations in that tier must quarantine for 10 days.
The Times reported that German Chancellor Angela Merkel wants the European Union (EU) to ban all UK travellers from entering the bloc.
The plan will be discussed by the EU’s integrated political crisis response committee, according to the newspaper.
Prime Minister Boris Johnson will meet Ms Merkel at Chequers on Friday.
Meanwhile, Malta will be added to the UK’s green list on Wednesday, but the central Mediterranean country announced that from that day it would only permit UK visitors who were fully vaccinated.
Children under 12 would be allowed to enter if they were accompanying parents or guardians who had had both doses.
Those aged between five and 11 would also have to show evidence of a negative PCR test taken within the previous 72 hours.
The Spanish authorities are introducing new restrictions on UK visitors to the Balearic Islands, which include Ibiza and Mallorca.
Prime Minister Pedro Sanchez told radio network Cadena SER that travellers who were not fully vaccinated must have taken a recent negative PCR test.
The change would be enforced within 72 hours, he said on Monday morning.
This means it will be in place when the Balearic Islands are added to the UK’s green list on Wednesday.
Hong Kong has put the UK on its “very high risk” list, meaning it has banned arrivals from the UK unless the person is a Hong Kong resident, or a spouse or child of a resident.
The territory has also announced a ban on direct flights from the UK from Thursday.