They’ll need to show either a valid British passport or a digital Certificate of Entitlement (COE) to prove their UK citizenship. The change is expected to affect more than 1.2 million people worldwide.

New rules: Prove your UK citizenship or risk being denied boarding

The law marks a big change from before, when dual citizens could simply use whichever passport was most convenient. Starting at the end of February, airlines will be required to check that anyone claiming to be a British national has either a valid UK passport or a Certificate of Entitlement (COE) linked to their UK Visas and Immigration account. Passengers who cannot show these documents will be refused boarding.

A UK passport costs about £97 (a little over €110) and can take three to six weeks or longer to be processed if you’re applying from outside the UK. The Certificate of Entitlement (COE), by contrast, doesn’t expire but comes with a higher price tag of around £560 (roughly €650) and requires a biometric appointment. According to the UK government, applicants who submit their documents online and by post can expect a decision within about eight weeks.

The new rule is already causing confusion and frustration, especially for travellers with short-term plans. Older passengers may struggle with online and digital processes, creating extra challenges for both airlines and travellers. Some dual nationals have criticised the way the regulations were communicated, saying it’s unclear what the rules are and who is enforcing them.