A BBC journalist with dual British-Iranian nationality has been prevented from flying to the US after falling foul of changes to visa rules.
Rana Rahimpour was told by US authorities she could not travel under a visa waiver scheme.
Under new laws, dual citizens from several nationalities must instead apply for a visa at the US embassy.
But Ms Rahimpour said advice from the embassy on whether the rules had been implemented was unclear.
The UK foreign office website says the rules come in on 1 April, while the US State Department website says the authorities have “begun the process of implementing changes” to the waiver scheme.
It was only after contacting the agency overseeing the waiver while at the airport, that Ms Rahimpour – a presenter at the BBC’s Persian service – was told her nationality excluded her from travelling.
Two of her cousins were also prevented from flying. They had all been due to travel on the flight from Heathrow to a family birthday in the US.
Ms Rahimpour described the new rules as “very unfair”, pointing out they restrict Iranians who have gained their nationality through marriage or parentage.
She tweeted: “My fully #British daughter can’t attend her #American cousin’s bday cos her mum was born in #Iran.”
The new rules, which also affect Iraqi, Syrian and Sudanese dual citizens, have sparked anger.
They were enacted in the wake of raised security concerns following the Paris attacks, but a joint statement from European ambassadors warned of dual nationals being “disproportionately and unfairly affected”.