Heathrow Airport in London said Portugal's sudden removal from the green list risks sending a message that the UK "remains isolated from the rest of the world".
It was one of many furious reactions from the travel industry to Thursday's decision to move Portugal on to the amber list only two weeks after it was designated a quarantine-free destination. Egypt and Bahrain were among the countries added to the red list.
Portugal was the only European holiday spot on the green list, which from Tuesday will contain only 11 countries and territories.
Ministers said the measure followed increasing concern about the spread of the Indian coronavirus variant and another potentially dangerous mutation, the Nepalese variant.
Heathrow Airport boss John Holland-Kaye said the decision represented another “lost summer” for tourism.
“Ministers spent last month hailing the restart of international travel, only to close it down three weeks later, all but guaranteeing another lost summer for the travel sector,” he said.
“Britain is the worst performing economy in the G7, and in the week that the prime minister hosts G7 leaders to launch his government’s vision of Global Britain, he’s sending a message that the UK will remain isolated from the rest of the world and closed to most of its G7 partners.”
Transport Secretary Grant Shapps suggested it could be mid-August before Europe caught up with Britain’s vaccination programme, which would then allow travel restrictions to be eased.
All of Europe is on the amber list, meaning travellers have to quarantine at home for 10 days upon return and take several Covid-19 tests. The government advises against travel to amber list countries unless for exceptional reasons, which do not include holidays.
Seven countries – Afghanistan, Bahrain, Costa Rica, Egypt, Sri Lanka, Sudan and Trinidad & Tobago – will move from the amber to the red list from Tuesday, requiring 10 days costly quarantine in a hotel on return. Only travellers who have British or Irish citizenship or residency rights can enter the UK from these countries.
Package holiday company Tui UK said the government broke its promise on the return of international travel.
“The government decision to move Portugal straight from green to amber will do untold damage to customer confidence,” managing director Andrew Flintham said.
“We were reassured that a green watch list would be created and a week’s notice would be given so travellers wouldn’t have to rush back home. They have failed on this promise.”
The decision wiped more than £2 billion ($2.8bn) off the value of UK-listed travel and airline companies.
EasyJet, British Airways owner IAG, Ryanair, Tui, Wizz Air and engine maker Rolls-Royce all suffered heavy falls.
Johan Lundgren, chief executive of easyJet, echoed concerns about the UK’s isolation.
“The government has torn up its own rulebook and ignored the science, throwing people’s plans into chaos with virtually no notice or alternative options for travel from the UK,” he said.
“This decision essentially cuts the UK off from the rest of the world.”
Communities Secretary Robert Jenrick said the government was taking a cautious approach to avoid jeopardising plans to lift social distancing restrictions on June 21, amid increasing concern over new Covid-19 strains.
Public Health England said the Nepal variant was detected in several countries, including a small number of cases in the UK.
It is investigating the mutation to better understand whether it could be more transmissible and less effectively tackled by vaccines.
"Imagine how worried we would be if this was the variant which was able to defeat our current vaccines,” Mr Jenrick told Sky News on Friday.
“There is no reason to believe that right now, but let's be cautious and do the research before making a judgment."