Double the usual number of flights to the UK are due to leave Portugal as holidaymakers scramble to leave on the last day before the country moves to the amber travel list.
Thirty-nine flights were due to depart from Faro Airport in the Algarve for the UK on Monday, nearly twice as many as are scheduled on a normal day.
Travellers must arrive in the UK before 4am on Tuesday or they will be required to self-isolate at home for 10 days due to a government decision to remove Portugal from its COVID green travel list.
Tourists hoping to beat the deadline are being hit by a combination of many flights being sold out, and the handful of available seats being sold at inflated prices.
Ryanair is charging £285 for a flight from Faro to Bournemouth on Monday, but just £17 on Wednesday.
EasyJet flights from Faro to Gatwick are £227 on Monday and £53 on Tuesday.
Tourists in the Algarve have also reported difficulties obtaining the pre-departure tests required by the government for people arriving in the UK.
Many holidaymakers and travel firms expressed anger when the announcement on Portugal was made last Thursday, as it came just 17 days after the ban on international leisure travel was lifted.
Portuguese authorities also questioned why the UK switched the popular holiday destination from its travel green list to amber, saying they could not “understand the logic”.
The Department for Transport, however, maintained the situation in the country “required swift action to protect the gains made with the vaccine rollout”.
It said the positivity rate for coronavirus tests in Portugal had nearly doubled since the travel lists were first created four weeks earlier.
Separate Test and Trace figures show that of 200 arrivals from Portugal who were tested between 6 May and 19 May, three were positive for COVID-19.