Portugal is set to be removed from the UK travel corridors list, as Covid-19 cases in the country exceed 20 per 100,000.
Pressure is mounting on England to consider imposing quarantine rules on travellers arriving from Greece amid reports of people returning with coronavirus.
Rising Covid cases prompted the Scottish Government to announce travellers from Greece would have to self-isolate for 14 days from Thursday, while Wales began asking arrivals from the island of Zante to enter quarantine.
The UK’s biggest tour operator Tui has suspended its holidays to the resort of Laganas on Zante.
But Greece has insisted it is doing “everything in our power” to keep UK holidaymakers safe.
It comes as rising cases in Portugal were prompting many UK tourists to pay hundreds of pounds to fly home before Saturday.
In recent weeks, the Department for Transport (DfT) has announced changes to its quarantine exemption list on Thursday nights, with the new rules being imposed on Saturdays at 4am.
In Portugal, the seven-day coronavirus cases rate is 22.7, compared with 14.2 for the previous week.
A seven-day rate of 20 is the threshold above which the UK Government has considered triggering quarantine conditions.
There were 14.3 coronavirus cases per 100,000 people in Greece in the seven days to September 1, up from 14.1 a week earlier and a similar rate to the UK.
In Buckinghamshire, two groups of people have tested positive for coronavirus after returning from abroad – including a group of teenagers from the Marlow area who are reported to have been on a trip to Zante.
Buckinghamshire Council said some of them were pupils at Sir William Borlase’s Grammar School and all the affected households were self-isolating.
Tour operator Tui also said it was aware of a “small number” of positive Covid-19 test results following a flight from Heraklion in Crete to London Stansted on August 27.
One passenger on the flight, who had been contacted by NHS Test and Trace and asked to self-isolate, complained that “hardly anyone” on the flight had been wearing a mask.
The woman, who wished to remain anonymous, told the PA news agency: “Our flight was hideous, hardly anyone wore a mask and the crew didn’t do anything about it.
“We raised the issue twice with the cabin crew who still didn’t enforce it.
“My family is okay but we are having to self-isolate.
“I’m so sad for my son because he has to miss his first week back at school.”