Brits are scrambling to return to Portugal from the UK over fears it could be re-added to the Government's quarantine list.
Budget airline easyJet has even sold out all its flights from Faro, serving the Algarve, to UK airports on Wednesday, Thursday and Friday.
British Airways is selling flights from Faro to Heathrow on Thursday for a whopping £554, a journey that can be made seven days later for only £139.
Thousands of people have travelled from the UK to Portugal since the country was added to the Government's quarantine exemption list on August 22, with airlines increasing capacity to meet high demand.
But the 14-day self-isolation rule for arrivals from the country could return this week due to a rise in Covid-19 cases.
There were 22.3 coronavirus cases per 100,000 people in Portugal in the seven days to August 31, up from 14.5 a week earlier.
A seven-day rate of 20 is the threshold above which the UK Government considers triggering quarantine conditions.
Chris Sainty, the British Ambassador to Portugal, said it has been "great to see people reunited with their families and enjoying the summer" but warned that "things can change quickly".
He urged travellers to "factor in the risks of travelling abroad in this fast-moving situation", adding: "Only travel if you are content to unexpectedly quarantine if required."
Another country currently on the exemption list, Italy, is recording a seven-day rate of 14.8 cases per 100,000, up from 10.0 a week ago.
In recent weeks the Department for Transport has announced changes to its quarantine exemption list every Thursday night, with the new rules being imposed every Saturday at 4am.
This has led to passengers rushing to return from destinations such as France, Switzerland and the Czech Republic.
The boss of British Airways' parent company has warned that reimposing the quarantine requirement for people returning to or visiting the UK from Portugal would cause further "chaos and hardship" for travellers.
Writing in The Times, Willie Walsh, chief executive of International Airlines Group, claimed the "ever-shifting list" means "the UK has officially hung up the 'Closed' sign".
He went on: "The Government is using arbitrary statistics to effectively ban 160 countries and in the process destroying the economy.
"The Government needs to introduce a testing regime to restore confidence."
In Ireland, the seven-day rate is 14.2, while in the UK it is 13.9. Figures have been calculated by the PA news agency based on data collected by the European Centre for Disease Prevention and Control.