More countries are set to be added to the red list amid concerns over high infection rates and the spread of Covid variants, an analysis shows.
Four countries have been identified as potential targets for when the Government this week publishes its updated list of countries rated green, amber and red, with the latter requiring returning Britons to quarantine in a government-approved hotel for 10 days at a cost of up to £1,750.
They are Bahrain, Costa Rica, Trinidad and Tobago and Kuwait, two of which are holiday destinations and two important Middle East economic connections, according to the analysis by Robert Boyle, a BA strategist who has previously correctly forecast destinations on the list.
It comes as Heathrow on Tuesday opened the UK's first dedicated terminal to process passengers arriving from high-risk red list countries and territories.
Heathrow will use Terminal 3 for direct flights from red list countries so passengers are processed separately from those arriving from amber and green destinations following criticism of infection risks from their mixing in immigration halls.
Ministers have warned travellers that countries could switch very quickly from green even with its new innovation of a "watch list" where a destination will be placed when rising infection rates put it at risk of turning amber.
"The watch list is an ideal, but a country could change colours very quickly. If something really dramatic happened with a super-variant, that will shut the place down very quickly. It won't be weeks. Ministers won't take any chances with it," said a source.
It follows criticism of the Government for allegedly placing political considerations over safety by failing to put India on the red list until weeks after it had banned travel from Pakistan and Bangladesh.
The four destinations all have higher infection rates than countries already on the red list. "Given how much heat the Government is taking about the delays in adding India to the red list, you might wonder why the four red list candidates haven't already been added," said Mr Boyle.
It came as France on Monday introduced a ban on any travellers from the UK unless they have "compelling reasons" to enter the country.
In a move aimed at preventing the spread of the Indian variant from the UK, travel to France from Britain will only be permitted for EU nationals, French residents or those travelling for essential reasons. Those who are allowed to make the journey must take a pre-departure Covid test and quarantine for seven days on arrival.
The UK's Foreign, Commonwealth and Development Office said the new French rules apply to all air, car, ferry and train passengers.
France is currently listed as an amber destination by the Government, which advises against travel there, with British authorities requiring people to self-isolate for 10 days and take two Covid tests on return.
The EU on Monday paved the way for quarantine and test-free travel for vaccinated people within the bloc by confirming its green certificate system will become operational from July 1.
This will mean any EU citizen travelling within the EU should be able to enter any EU country if they are fully vaccinated, or have a negative Covid test or evidence of immunity from having had the virus.
The EU has, however, yet to decide whether or when to add the UK to its white list of non-EU countries giving Britons the same rights of travel. The EU also retains an "emergency brake" to reimpose restrictions on countries with a surge in infection rates or Covid variants.
Only a handful of destinations are expected to be added to the UK's green list this week, with any reopening to major EU destinations likely delayed until at least the end of June.
Paul Charles, the chief executive of travel consultancy The PC Agency, said government pressure for a dedicated red list terminal was a good sign that it was prepared to expand capacity and see more passengers coming into the UK from green and amber destinations.