The move, which is due to be confirmed in a press conference with transport secretary Grant Shapps this evening, will throw the holiday plans of thousands of Brits into disarray.

Portugal was the only realistic holiday destination on the list for safe travel, with other popular hotspots such as France, Greece and Spain not on the list announced last month.

It is understood that Portugal has been moved to the amber list of destinations. People arriving in the UK from amber countries need to quarantine at home for 10 days and take PCR Covid-19 tests on or before day two and on or after day eight after returning home.

Anyone arriving back in England from a green list country will need to take a pre-departure test up to 72 hours before their return travel, and a single PCR test on or before day two of arrival into England. However, they will not need to quarantine.

It was hoped the list of countries on the green list would be expanded in today’s announcement – but that now looks unlikely with several media outlets reporting that no new countries have been added to the list.

Reports also note a strong expectation that more countries will be added to the red list. Arrivals in the UK from red list countries need to stay in hotel quarantine for 10 days at a cost of £1,750 per person.

As well as causing problems for Brits with holidays booked, removing Portugal from the green list will put jobs at risk. The Transport Salaried Staffs’ Association (TSSA) has repeatedly lambasted the government for failing to support travel agencies.

Manuel Cortes, TSSA general secretary, said: “We were all hoping to see more holiday destinations moving into the green list and none more so than the high street travel agencies who have suffered the hardest 16 months in living memory thanks to this Covid-19 pandemic.

“Of course, beating the virus is the most important, and moving Portugal to the amber list is the right thing to do if that’s what the science says. But the way this Tory government has bungled the decision means travel chaos as holidaymakers who went abroad in good faith, realise they’re at risk of an unexpected 10-day quarantine when they come back and many will now scramble to come back early.

“This is the last thing our struggling high street travel agencies needed. Summer 2020 was a nightmare of holidays cancelled at the last minute, the ‘safe’ list changing daily and sometimes hourly. Sadly, it seems like the Tory government hasn’t learned their lesson as Portugal has been abruptly moved to the amber list with almost no warning.

“The government needs to sit up and pay attention. Travel agencies cannot go on booking and cancelling holidays without support. If the industry is to survive then the government needs to step in and offer travel agents bespoke support as it has done with other industries such as hospitality and rail. Otherwise there’s a very real risk we will not have a travel industry left when this pandemic is done.”