MADRID — British and Spanish authorities moved to reassure UK nationals resident in Spain over their travel rights after several complained of being denied entry this weekend, amid pandemic restrictions and confusion over post-Brexit documentation.

The British Embassy in Madrid called on Spanish authorities to show flexibility following the passengers' distressing experiences. Some were allegedly refused permission to board a flight from London to Madrid, while others were reportedly put back on the plane after arriving in Barcelona.

"This should not be happening," the UK embassy said in a Facebook post.

The Spanish Embassy in London has moved to clarify the situation, reassuring UK nationals resident in Spain that the documents at the center of the controversy are indeed valid.

Under current coronavirus restrictions, Spain is limiting travel from the UK to Spanish nationals and people who are legally resident in Spain, until Jan. 19.

Meanwhile the post-Brexit transition period ended at New Year, heralding a change in travel and residency rules.

Max Duncan, a journalist, says he was among nine people who were not allowed to board a joint British Airways/Iberia flight from London's Heathrow Airport to Madrid on Saturday because they were told they did not have the correct documentation.

Both the UK government advice and Spanish authorities' information had previously said that residency documents — the Foreign National Identification (NIE) and a new version, the Foreign ID card (TIE) — would be valid after Brexit.

Duncan says the passengers were told at the airport that Spain was only accepting the new TIE card, contrary to the official advice.

Others took to social media to complain that the authorities in Barcelona were not accepting the NIE document.

Patricia Moody, a 69-year-old retiree who has called the southern Spanish town of Zurgena home for nearly four years, was among the group barred from boarding for Madrid.

Moody said she and her husband, who she says needs to see his doctor back in Spain, have spent £1,900 (€2,140) on getting tested for the virus, travelling 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.”

The Spanish Embassy in the UK issued a statement on Sunday afternoon, referring to the problems experienced by those denied boarding.

"The Certificado de Registro de Ciudadano de la Union Europea (also known as "green certificate") and the new "Tarjeta de identidad de Extranjero" are valid proof of residency for UK nationals who wish to return to their homes in Spain. All travelers must also carry a valid passport," the statement said.

It added that UK nationals who had started their application process for residency, but who did not yet have their new documentation, should also be allowed to board flights.

The Spanish government was introducing a seven-day grace period from Jan. 4, the Spanish embassy said.

The British embassy said in response that having been in contact with the Spanish authorities it was "pleased to share this important clarification".

Earlier it said that it had received "comments and messages from many UK residents in Spain", such as students and those caring for family members, who did not yet have the necessary documents under current restrictions.

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.

Spain has been rolling out the new TIE system to register permanent foreign residents but it’s suffering a backlog due to the high number of requests, according to Euronews.

Iberia responded to Euronews saying that it had received an email from border police on Jan. 1, stating that the EU registration document (the "green certificate") was not valid proof of residency for UK nationals.

The airline added that it then received a second email on Saturday at 7.30 p.m. saying that the document could be used if it wasn’t expired. — Euronews