Some have been blocked at airports as they attempt to travel to other EU countries, being told at the border that their documents are not in order.

"We are in desperate straits," Tig James, co-president of the British in Portugal campaign group, told Euronews. "It has paralysed and damaged UK nationals' lives emotionally, physically and financially."

James cites cases of British workers unable to sign work contracts, with some having job offers retracted, because of the lack of residency documentation — "most notably, five EasyJet pilots who had moved to Portugal, with their families, solely for that purpose".

"Two people were recently detained in Germany because of out-of-date residency documentation," she added. They had to buy alternative return tickets back to Portugal via another route outside the EU, at a cost of some €5,000.

The couple have employed a German immigration lawyer and are hoping for a court hearing. "They have done everything legally," James says.

Like British nationals living elsewhere in the European Union, the tens of thousands living in Portugal were guaranteed residency and associated rights under the Brexit divorce treaty.

As long as they had moved to the country before the new rules took effect in 2021, the UK-EU Withdrawal Agreement (WA) protects rights such as residency, housing, employment, health care and social security, for them and their family members.

The new rules covering travel state that UK nationals with residence rights in an EU country "do not need a visa to enter their country of residence or any other EU country". But they stress the importance of having new official documentation "in the form of a biometric residence card".

Tig James says the Portuguese authorities have been promising her that the new Withdrawal Agreement biometric cards (WABCs) would be arriving "soon" since July 2019. But three years on, they have yet to be issued.

In an email seen by Euronews, Portugal's Immigration and Borders Service (SEF) "clarifies that the current residence documents of British nationals living in Portugal continue to be accepted".

SEF explains that British residents can download proof of their application in the form of a supporting document with a QR code. This, it says, "allows to travel, serves as proof of their residence in Portugal and guarantees access to public health and social services".

But British resident Nicola Franks told Portuguese TV channel SIC that she encountered difficulties on a trip to Amsterdam with her husband this summer without a new biometric ID card.

"The border control official looked at these papers he had obviously never seen before and decided they were not legitimate, that, in fact, they were only applications for residency. To make a long and frightening story as short as possible, he turned me back to Portugal," she said.

"SEF are consistent in saying the paperwork they have given is sufficient which it most certainly isn’t," James told Euronews, arguing that the "dreadful consequences" are "devastating lives".

"Without a WABC you can’t register for health care if you move address (people seriously ill, potentially terminally ill, cannot get treatment), doctors refusing treatment, appointments cancelled."

She adds that "repeatedly" Britons have had problems trying to exchange UK driving licences for Portuguese permits to comply with the law. Tax offices and banks are refusing to change addresses, while car owners are unable to register, repair or import vehicles. Parents are forking out tens of thousands of euros because applications for EU university fees are being rejected.

"Portuguese institutions or businesses are simply refusing to deal with UK nationals or provide a service," James says.

"The Portuguese social security office has ceased family allowance payments until a WABC can be produced and the birth of a child cannot be registered. Only on one family employing a lawyer were they able to finally register their child and, by the time all the negotiations were completed, the child was ten months old."

British nationals have been unable to bring "third country" spouses into Portugal.

James cites the case of one man whose own residency document has expired and is waiting for his wife to be allowed in.

"He cannot get a renewal nor can he leave the country as he is not allowed to start the renewal process until his wife has her WABC. His mother is now seriously ill and he cannot leave to see her. In the meantime, as his residency has expired, his dermatologist has refused to see him for his skin condition. Families are being torn apart," she says.

"The reasons for the three-year delay by the immigration department? Staff shortages, holiday periods, the pandemic, and now Ukrainian refugees," James explains.

A pilot programme has been set up by SEF to process biometric data for Britons living in the Azores and Madeira. But this concerns only a fraction of the overall number of UK nationals in Portugal.

The immigration and borders service says staff training in collecting biometric data will begin "very soon" and Britons will begin being issued with their new cards. But Tig James says she has heard that the programme has still to get off the ground.

The campaigner adds that she has been lobbying British and Portuguese politicians for years, but "all that has happened is the situation has got worse".

"SEF are wilfully, deliberately and systemically not adhering to the Withdrawal Agreement resulting in the physical, emotional and financial suffering of thousands of UK nationals in Portugal."

James has turned down an appointment in September to present evidence of the Britons' difficulties before the European Commission's Economic and Social Committee.

"My residency has expired and we already have incidents of UK nationals having terrible problems in Brussels trying to leave as their documentation, as is mine, is out of date, expired, being detained. I cannot afford to get arrested," she says.