People with a British passport are allowed to use the e-gates to scan their documents at border control for passengers arriving at Lisbon, Faro, Porto and Funchal (Madeira) airports.
This is designed to ensure that passengers do not wait a lengthy period of time to get to the other side of the airport.
But the Foreign Office has issued a warning ahead of a busy holiday period for the European nation this summer.
Officials have urged passengers to get their passports stamped to avoid an awkward conversation with border officers.
It writes: “E-gates are in operation at Lisbon, Faro, Porto and Funchal (Madeira) airports for use by British and some other non-EU passport holders.
“On arrival or departure, check you are eligible to use the e-gates and that you are in the right queue.
“A border officer may also stamp your passport after you have passed through the e-gate; this is for airport operational reasons.
“Check your passport is stamped by the border officer when you enter and exit Portugal as a visitor.”
It adds: “Border guards use passport stamps and e-gate records to check you’re complying with the 90-day visa-free limit for short stays in the Schengen area.
“If relevant entry or exit stamps are not in your passport or visible to a boarder officer on the computer system, a border officer may presume that you have overstayed your visa-free limit.
“If you are missing entry/exit stamps, you can show evidence of when and where you entered or exited the Schengen area and ask the border officer to add this date and location in your passport.”
A number of Covid entry requirements are in place for UK holidaymakers heading over the Portugal.
For entry, passengers must show proof that they are fully vaccinated or show evidence of a recent negative test.
Millions of people from the UK are expected to catch up on trips abroad this year as restrictions continue to lift across the globe.
HM Passport Office has already seen an ‘unprecedented demand’ for vital travel documents this year.
It is expected that 9.5 million British passport applications will be sent through in 2022.
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