The democratic vote to leave the European Union has had many unexpected consequences for travellers. One of the most serious: UK passengers wrongly denied boarding by their airlines because their passports are deemed no longer valid after Brexit.

So rife is the problem that my “pinned post” on X (formerly Twitter) reminds travellers, and airlines that a UK passport must meet two conditions for travel to the European Union (and wider Schengen area):

Seeking to inform the travelling public about the rules that our government signed up for has been one thing. I then last year spent several weird months explaining to our government the agreement it had made with Brussels.

The Foreign Office and Home Office initially insisted that British passports expire after nine years and nine months, a fiction briefly extended to claim that children’s UK passport were no good after four years, nine months.

Eventually, in May 2022, officials and ministers conceded that I was right and changed government advice. By then, I thought I had also persuaded the airlines about the rules, with Ryanair and easyJet last to fall into line.

Yet deep into 2023, ground staff at UK airports are still turning passengers away needlessly – causing distress to travellers and triggering hundreds of pounds in compensation.

In November, British Airways staff at London Heathrow stopped Laura Savage catching her flight to Oslo, while in December Mark Starkey was turned away from a dawn Ryanair flight from Luton airport to Alicante.

Each time cases like these appear, it has the welcome effect of informing previous victims of wrongful denials of boarding to come forward. Here is Camilla, who in February last year was refused boarding a flight for a three-day trip to Italy. Her airline claimed she needed six months remaining on my passport to travel.

“My passport was issued on 1 May 2012 and expired on 1 July 2022,” Camilla says. “Can you confirm that I was wrongly turned away? If so, what do I do about claiming compensation?”

Camilla’s passport was valid for travel to the EU until 1 April 2022; all travel would have to be completed by that date because of the “three-month rule”. So Camilla was compliant. But how much cash is she due, and how can she get it back?

Under European air passengers’ rights rules – known as EU261 – she is entitled to £220 in denied boarding compensation, plus a refund of her return airfare. It should be a simple matter to claim the stipulated cash and cost of the ticket through the airline’s online portal for claims, supplying a scan of the dates of the passport.

If the carrier has any sense it will accept the claim and pay out. The airline may try to deflect the claim on the basis that it had relied on the inaccurate travel advice the UK government was putting out.

However, I told all the major airlines (and the UK government) in the autumn of 2021 exactly what the European rules were. I provided all the contact details for the relevant officials in Brussels and invited the carriers to check my work. Choosing to follow the flawed guidance of a non-EU government rather than the precise specification of an EU body looks like a feeble defence.

Claiming sums beyond that, whether for wasted costs of travel to the airport or for pre-paid accommodation abroad, will be trickier; airlines tend to say they are not liable for “consequential losses”. In my opinion, that is not a justifiable defence, but a successful claim might involve a legal battle.

Anyone whose claim is refused can go to alternative dispute resolution (ADR). But arbitrators, in my experience, sometimes get things wrong. Fortunately, if a decision goes against you there is nothing to stop upgrading to Money Claim Online.