British dual nationals may be able to use expired UK passports to prove to airlines they are British when controversial new immigration rules come into force, the Home Office has said.

The new rules, coming into force next Wednesday, require anyone coming into the UK with British dual nationality to present a British passport when boarding a plane, ferry or train or to have a “certificate of entitlement” costing £589 attached to their foreign passport.

Airlines and other transport operators risk being fined if they board passengers who do not have the right to enter the destination country.

The rules have caused stress, disgust and bafflement among Britons with imminent travel plans whose passports have expired or who do not have a British passport, including children born abroad.

The Liberal Democrats have called for a grace period to allow people affected by the change to get new passports, a process that could take many weeks.

The Lib Dems’ immigration and asylum spokesperson, Will Forster, said the changes had left many dual nationals “in the lurch”. He said: “Whilst they sort out the chaos, the government should allow a grace period, as many dual nationals are in heartbreaking circumstances, unable to visit ill family members or attend weddings and funerals. They must also urgently provide a low-cost, affordable alternative to the current system.”

People with British and Irish dual nationality are not affected by the rule changes.

In a statement on Thursday, the Home Office said airline carriers could, “at their own discretion” accept an “expired British passport as alternative document”. This would be in addition to the valid foreign passport that would be sufficient were it not for the new rules.

It said of the rule change: “We recognise that this is a significant change for carriers and travellers, but we have been clear on requirements for dual British citizens to travel with a valid British passport or certificate of entitlement, in line with those for all British citizens.

“At their own discretion, carriers can accept an expired British passport as alternative documentation. Separately, individuals who have previously had a British passport can apply for an emergency travel document if they urgently need to enter the UK.

“In line with current practice, on arrival at the UK border, Border Force will still assess a person’s suitability to enter the UK and conduct additional checks if required.”

Many citizens either living overseas or with dual nationality and living in the UK have been caught by surprise by the rule change.

The Home Office points out that the new system, designed to separate British nationals from foreign nationals at border controls, has been flagged on the gov.uk website since October 2024 when it announced the introduction of the “electronic travel authorisation” that foreign nationals without residency rights must now get to enter the UK.

It announced in November that under the new rules British dual nationals would not be able to get an ETA on a foreign passport.

Morgan Read, an immigration barrister at North Square chambers, said there was nothing in the Immigration Act 1971 requiring a valid UK passport to prove British citizenship. “It is well established that expired passports can be used to prove citizenship and identity – that’s not their purpose, but they can be used for that,” he said, pointing to the official government page on “right to work” checks for British or Irish citizens that allows expired passports.

Hundreds of British people living abroad have written to the Guardian complaining they have not had time to get a new passport for travel at the end of February or March. One man cancelled plans to go to his father’s memorial service; others have brought forward plans to see dying relatives before the rule change kicks in.

Other British nationals living in the EU said they had in effect been forced to take dual nationality after Brexit and had had no reason until now to keep their British passport up to date as they could travel around Europe and in and out of the UK on their EU passport.