The cost of flights to some of the most popular holiday destinations rocketed on Thursday night ahead of the government's announcement of its travel "green list".
Prices for flights to Portugal's resorts more than doubled in two days after suggestions that it could be included on the quarantine-free "green list" when the ban on foreign travel is lifted on May 17.
The country is the only big European holiday destination for Britons with a chance of inclusion on the list, to be unveiled by Grant Shapps, the Transport Secretary, at a Downing Street press conference on Friday afternoon.
Ministers on the Cabinet's Covid operations committee will meet on Friday to decide which countries should be red, amber or green based on their vaccination rates, prevalence of Covid and its variants and their capacity for analysing the genome of the virus.
Government sources maintained that the "green list" would contain a "handful" of countries, many of which will have travel restrictions or could even be shut to tourists.
However, that has not stopped a surge in demand for flights, pushing up prices – particularly to Portugal. It follows the disclosure that the Foreign Office had lifted its advice against non-essential travel to the country along with Rhodes, Kos, Zante, Corfu, Crete and the Canary Islands.
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British Airways was on Thursday night charging £530 for a flight from Heathrow to the Algarve on May 17, compared with £234 for the same route two days earlier.
A Ryanair flight from Stansted to Portugal's capital Lisbon on May 17 was £152, compared with £15 on May 16. And EasyJet was charging £234 for a flight from Luton to the Algarve on May 17, when it had been just £73 the previous day.
"People are gambling on the country being rated green, knowing that they can rearrange their flights until the assessment changes, or accept the fact that it is amber and that they have to quarantine on their return," said an industry source.
Most of the popular European countries including Spain, Greece, France and Italy are expected to be on the "amber list", requiring returning travellers to quarantine for 10 days and pay for PCR tests on days two and eight.
Mr Shapps is expected to signal that the "green list" will only start to expand after reviews in three and six weeks, which means European tourist hotspots could be open to holidaymakers by the end of June.
A government source said: "It is about a slow and cautious return to travel. It is a global issue and not something we can do on our own. Just because our citizens have been vaccinated doesn't mean they don't have to follow other people's rules."
Malta, one of the prime candidates for the "green list", is not due to open its borders to tourists until June 1, when they will have to show proof of vaccination or a negative Covid test result.
Israel, another candidate, will only accept vaccinated holidaymakers and requires a test for biological proof that visitors have been jabbed. Travel to the country is expected to be limited to select group tours from May 23 and only opened to independent tourists from July.
Australia, New Zealand and the US are all shut to foreign passport holders even if they make the "green list" because of their near-zero infection rates or vaccination numbers comparable to the UK.
Iceland, another prime candidate, requires even vaccinated travellers to quarantine until they have taken a PCR test to prove they are negative for Covid. Other visitors are required to take a test on arrival and quarantine until a second negative test result on day five or six.
Gibraltar is one of the few "green list" contenders that will allow Britons without a PCR test, but has limited capacity for any surge in tourists.
Ministers could, like last year, include some or all of the 14 British territories but some – Anguilla, British Virgin Islands, Cayman Islands, Falklands, Saint Helena, Ascension and Tristan da Cunha, and South Georgia and the South Sandwich Islands – currently require quarantine on arrival.
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