Portugal will be removed from the green travel list on Thursday, it has been reported.
The summer hotspot will be put on the amber list following a meeting between the Westminster and devolved governments, and the Joint Biosecurity Centre, according to the BBC.
People returning to the UK from amber list countries must self-isolate at home for 10 days as part of coronavirus restrictions.
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Many holidaymakers in Portugal face a scramble for flights home before the move is introduced, which is expected to be in the coming days.
The Government's decision is a huge blow for the travel industry, as Portugal was the only viable major tourist destination on the green list when it was announced last month.
The PA news agency understands no additions will be made to the list on Thursday, despite speculation that Spanish and Greek islands and Malta could be added.
Additions to the red list are expected on Thursday, with Bahrain, Costa Rica, Malaysia, Thailand among the potential candidates.
People returning to the UK from red-list locations must stay in a quarantine hotel at a cost of £1,750 for solo travellers.
Paul Charles, chief executive of travel consultancy The PC Agency, said the failure to add to the green list is a "terrible decision".
He told PA: "They are basically putting at risk tens of thousands of jobs across aviation and the travel sector, and not showing any signs of helping the sector to recover.
"They seem to want to continue to create an atmosphere of fear among travellers, which is totally at odds with other countries.
"There are several countries which meet the criteria to be on the green list so this is clearly a politically charged decision rather than one based on data."
