MADRID (AP) — Blame COVID-19 travel restrictions or Brexit but whatever the cause, some British citizens trying to return to their homes in several European countries this weekend have been barred from boarding flights.

Airlines refused documents that before Brexit had been valid proof of the Britons' status as residents in Spain, Italy and Germany, although Spanish authorities claimed that the issue had been resolved by mid-Sunday.

Their ordeal came amid heightened travel restrictions due to a coronavirus variant that has been blamed for faster contagion in the U.K. and highlights the bureaucratic complexities resulting from Britain's departure from the 27-nation European Union.

Both Spanish and British authorities said Sunday that the green-colored certificate of EU citizenship with a foreign national identification number issued by Spain is still valid for British citizens residing in Spain under the bilateral provisions that followed the U.K.’s withdrawal from the bloc on Dec. 31.

But the travelers say British Airways and Iberia, which are part of the IAG group, have been refusing to let them board for the past two days.

Iberia said in a statement late Sunday that a communication from Spain's border police on Jan. 1 had created “some confusion” and that it was later clarified. British Airways didn’t immediately respond to requests for comment.

Around 300,000 British citizens are registered as permanent residents in Spain, although before Brexit, many more had been living full or part-time in the country without officially registering.

Patricia Moody, a 69-year-old retiree who has called the southern Spanish town of Zurgena home for nearly four years, was among a group of at least nine people unable to board a Madrid-bound BA/Iberia flight from London’s Heathrow Airport on Saturday.

Moody said she and her husband, who she says needs to see his doctor back in Spain, have spent 1,900 pounds ($2,600) on getting tested for the virus, traveling to the airport and booking new tickets after they were refused boarding. Their second attempt was also futile.

“Throughout all the months of negotiating Brexit, we were always assured that nothing would change for us,” she said. Referring to the airlines and authorities in both countries, she added: “It’s horrendous and we are suffering because of their incompetence.”

Following the discovery of the coronavirus variant in the U.K., many European nations have banned all travel from the British isles except for their own nationals and U.K. citizens with residency rights.

Travelers to Pisa, Italy, and Berlin have also reported similar hurdles in boarding planes operated by Ryanair and Lufthansa despite carrying documents that had been accepted by the Italian and German governments, respectively.

Matt Bristow, a spokesman for the British in Germany association of residents in that country, said: “This appears to be a case of U.K. airport staff not knowing what documents to accept or applying the rules more stringently than the German border police would."

Spain has been rolling out a new system to register permanent foreign residents called TIE but it’s suffering a backlog due to the high number of requests. Authorities told AP that proof of application for the TIE and the “green certificate” for EU citizens were still valid to travel for British residents under the new health restrictions in place until Jan. 19.

“This should not be happening,” said the U.K. embassy in Spain said in a Facebook post. “The Spanish authorities have today re-confirmed that the green residency document will be accepted for travel to return to Spain, as stated in our travel advice.”

But Sam Dakin, a 32-year-old English-language teacher based in Barcelona for the last four years, and his partner, who has been in the Spanish city for 8 years, said they needed more assurances before they could rebook flights.

The couple had been blocked from flying Saturday morning despite carrying their certificate and then were refused boarding on another flight Saturday evening that British Airways had initially said they could take.

“Just because the government adviser said that we could travel, we don’t know whether that will happen when we turn up at the counters," Dakin said. “We just don’t know where we’re going to get answers."

In a statement, Spain's Foreign Ministry said there had been “an isolated communication problem with some airlines that affected a very small number of travelers” and that air traffic between the U.K. and Spain was proceeding “with normality" by mid-Sunday.

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AP writer Geir Moulson in Berlin contributed to this report.