LONDON — British dual citizens could find themselves barred from entering the UK in two days if they lack a British passport. New Home Office rules, effective February 25, demand proof of British citizenship amid rollout of the Electronic Travel Authorisation system.

The ETA applies to visitors from countries not requiring visas. British and Irish citizens stay exempt. Dual nationals, however, must now present a UK passport or a certificate of entitlement attached to their foreign passport. Airlines face fines if they board passengers without proper documents, giving carriers leeway to deny travel.

A UK passport renewal online runs £94.50. The certificate of entitlement costs £589, according to Home Office fees. Previously, dual nationals entered freely on foreign passports. That ends Wednesday. All other nationals from their second country now need an ETA, which dual Brits cannot obtain.

Officials define dual nationals as those holding British citizenship alongside another from birth, UK-born people who later gained foreign citizenship, or naturalized Brits retaining prior nationality. Those abroad can seek emergency travel documents from British embassies to return home.

The Home Office has cautioned for months about pre-departure checks. Airlines must verify eligibility before flights. Ryanair indicated it might accept an expired British passport as proof. Still, carriers hold final say and risk penalties for errors.

Irish citizens dodge the requirements. The Common Travel Area pact lets them travel, live and work in the UK on Irish passports alone. No ETA needed, and border checks from the Republic of Ireland remain rare.

Reactions split online. Cesare, an Italian maths lecturer naturalized in Britain in 2023 after moving here in 2016, called it another post-Brexit burden. “Everyone ends up paying the price of measures like ETA,” he said. “While ETA is just for visitors, now everyone who is not a visitor also needs to prove that.”

Others see alignment with global norms. The US runs its ESTA waiver program. The EU plans ETIAS for third-country travelers later this year. One Facebook commenter put it bluntly: “It’s a privilege to have dual citizenship. Just keep both passports up to date and enter and exit on the appropriate country’s passport.”

Dual nationals have until Tuesday to prepare. Home Office guidance urges valid British passports or certificates for smooth entry. The shift aims to streamline checks as ETA launches for 74 million expected annual visits from exempt nations.

Applications for certificates take up to 15 weeks by post or three weeks at a premium center. Passports process faster online. Border Force officers at ports like Heathrow and Dover will enforce the rules, potentially turning back non-compliant arrivals.