ITV News Consumer Editor Chris Choi spoke to UK tourists in Portugal about what the change means for them
Portugal will be moving to the amber list and no new destinations will be added to England's green travel list, Transport Secretary Grant Shapps has confirmed.
This means anyone travelling back from Portugal to the UK - from 4am on Tuesday June 8 - would have to spend 10 days in quarantine and ensure they can pay for two PCR tests.
It is likely to spark frustration amongst those who have booked trips to the country - including those who travelled to Porto for the Champions League final as well as Brits travelling to popular tourist destinations such as the Algarve.
Grant Shapps warns of a new Covid mutation as Portugal is removed from green travel list
Mr Shapps said it was a "difficult decision to make", however added two things caused concern for the UK government.
The government said the decision to move Portugal to the amber list followed an "almost doubling" in the country’s Covid-19 test positivity rate and the discovery of 68 cases of the Delta variant including some with a mutation previously seen in Nepal.
Mr Shapps said: "One is the positivity rate which has nearly doubled since the last review in Portugal and the other is there's a sort of Nepal mutation of the [Delta] Indian variant which has been detected.
ITV News Correspondent Juliet Bremner reports from Corfu, which expected to make England's green list on Thursday
"We just don't know the potential for that to be a vaccine defeating mutation and simply don't want to take the risk as we come up to the 21 June and the review of the fourth stage of the unlock."
Afghanistan, Bahrain, Costa Rica, Egypt, Sri Lanka, Sudan and Trinidad and Tobago are to be moved to the red list
However, Labour has said the UK government have "caused chaos with the mishandling of travel restrictions at the border", before calling for the amber list to be scrapped.
What are the rules for people returning from each category?
Green: There is no need to self-isolate. Take a pre-departure test and a PCR test on day two of your arrival in the UK.
Amber: Self-isolate for 10 days, unless you receive a negative result from a test taken at least five days after arrival. Take a pre-departure test, and PCR tests on day two and day eight of your arrival in the UK.
Red: Spend 10 days in a quarantine hotel. Take a pre-departure test, and PCR tests on day two and day eight of your arrival in the UK.
In a statement, Nick Thomas-Symonds MP, Labour’s Shadow Home Secretary said: "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."
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Summer hotspots such as the Spanish and Greek islands plus Malta had hoped to be awarded green status on Thursday, but no new additions have been made as Covid cases continue to rise.
EasyJet chief executive Johan Lundgren has criticised the latest update on travel lists, saying it "makes no sense".
Consumer Editor Chris Choi explains the consequences the travel announcement will have on the industry
Responding to the latest changes, he said: "This shock decision to add Portugal to the amber list is a huge blow to those who are currently in Portugal and those who have booked to be reunited with loved ones, or take a well-deserved break this summer.
"With Portuguese rates similar to those in the UK it simply isn’t justified by the science."
Mr Lundgren added: "And to add no more countries to the green list when most of Europe’s infection rates are on a downward trend and many places with low infection rates below that of the UK, such as the Balearics with a current rate of 33 in 100,000 and Malta, with just 12 in 100,000, this makes no sense.
"Especially when domestic travel is allowed within the UK, despite a number of cities having infection rates 20 times greater than much of Europe."
Meanwhile, Boris Johnson warned on Wednesday the government will have "no hesitation" over moving countries off the green list if necessary.
The prime minister also said it will be a case of "wait and see" what the recommendations of the Joint Biosecurity Centre are before announcing changes to the travel lists.
Holidaymakers returning from amber list locations, which includes popular hotspots such as Spain, France, Italy and Greece must quarantine at home for 10 days and take two post-arrival tests, while there is a travel ban to red list countries.
However, people returning to the UK from green locations are not required to self-isolate, and only need to take one post-arrival coronavirus test.
Stay up to date with the changing travel situation in the UK and abroad with news, information and advice at itv.com/holidaynews