Hopes of a summer holiday abroad have been dashed as no new countries have been added to the UK's green travel list and Portugal has moved to amber.
No further countries are being moved from the amber to green status and travellers returning from Portugal will have to quarantine following the review of the government's travel traffic light system.
Seven countries are also being added to the red list from the amber list. They are: Afghanistan, Bahrain, Costa Rica, Egypt, Sudan, Trinidad and Tobago, and Sri Lanka.
The change will come into effect at 4am on Tuesday 8 June.
The Department for Transport (DfT) said the measures are being implemented "to safeguard public health against variants of concern and protect our vaccine rollout".
Transport Secretary Grant Shapps said it was "a difficult decision" and Portugal was downgraded because the government wants to give the UK "the best possible chance of unlocking domestically" on 21 June.
He said the emerging Nepal mutation of the Indian variant was of concern and Portugal's positivity rate has "nearly doubled since the last review".
There were hopes some Greek and Spanish islands, and Malta could have been added to the green list in the first review of the system since it came into play three weeks ago.
Portugal was the only major holiday destination on the 12 country green list, meaning tourists could return to the UK without having to quarantine.
Nearly 20% of Portugal's population has been fully vaccinated and cases are relatively low but have been increasing over the past week.
Madeira and the Azores are also moving with mainland Portugal from green to amber.
People arriving in the UK from amber list countries have to take two post-arrival tests on day two and day eight after arriving and self-isolate at home for 10 days, although they can reduce that time if they take an additional negative test on day five.
Those returning from green locations are not required to self-isolate but they must take one post-arrival coronavirus test.
Shadow home secretary Nick Thomas-Symonds said the government has "caused chaos with the mishandling of travel restrictions at the border".
Mr Thomas-Symonds added: "The confusion over the 'Amber List' has led to reports of over 50,000 people travelling to the UK daily, with only a tiny percentage going into hotel quarantine and a stream of flights entering the UK from 'Amber List' countries.
"Labour has warned time and time again that this is leaving the door wide open to new strains of the virus.
"Moving Portugal onto the 'Amber List' is not the answer. The 'Amber List' itself should be scrapped.
"Ministers also now need a clear plan to manage the confusion that will result in Portugal being removed from the 'Green List' so quickly and must publish all of the data behind this decision."
Meanwhile, in a tweet, the Portuguese foreign ministry said it could not understand the "logic" behind the UK Government's decision to move Portugal to the amber list.
UK Health Security Agency chief executive Dr Jenny Harries said: "Increases in case rates in the UK serve as a reminder that this pandemic is not over yet and we need to take a cautious approach.
"Everyone should observe the travel guidance, continue to follow hands, face, space and fresh air, and have both doses of the COVID-19 vaccine when offered."
Shares in airlines easyJet and British Airways and travel companies TUI and Jet2 fell on fears Europe would lose another peak travel season, when millions of Britons usually head to southern Europe.
The industry has already been weakened by 15 months of lockdowns and many companies - and countries - had been hoping for a summer boom as the UK has one of Europe's highest vaccination rates, with 75% of adults having one dose and 50% having two.
Lockdown restrictions are easing across the UK but the Indian variant, also called the Delta variant, has caused concern.
The British Airline Pilots Association (BALPA) said: "This excessive caution could be the final nail in the coffin for the travel industry which has borne the economic brunt of the COVID-19 crisis with no help from the government."
BALPA's acting general secretary Brian Strutton said: "This decision is a total disaster for the already fragile travel industry and is likely to lead to further airline failures and many more job losses.
"We understand that safety comes first, but with vaccination programmes going well in many countries, it seems the government is ignoring the evidence and is allowing safe countries to languish in the amber and red categories for no valid reason.
"Any shred of public confidence is in tatters and the traffic light system seems stuck on red.
"Our airlines need this summer season if they are to survive. The government must look at the evidence and stop this illogical, over-cautious approach, that is killing a once-thriving industry."
Ahead of the list announcement, Health Secretary Matt Hancock warned: "We have got to follow the data and of course, I understand why people want to travel but we've got to make sure we keep this country safe, especially because the vaccine programme is going so well.
"We have seen hospitalisations and deaths come right down and we have to got to protect the progress we have made here at home, whilst allowing for travel where it is safe.
"You have got to follow the data."
On Wednesday, Boris Johnson said the government will have "no hesitation" in moving countries off the green list if necessary.
Each country is assessed based on a range of factors, including what proportion of a population is vaccinated, rates of infection, emerging new variants, and access to reliable scientific data and genomic sequencing.
Source: Sky News