The Iranians are holding three more Britons as well as Nazanin Zaghari-Ratcliffe amid claims of a vendetta against Theresa May, it has emerged.
Tehran is said to have been left furious when the Prime Minister detained and deported two of its officials when she was Home Secretary in 2013.
Today it emerged that up to four dual British-Iranian nationals are in jail there, including Mrs Zaghari-Ratcliffe who was imprisoned last year.
Another Briton in the notorious Evin jail near the capital is grandfather Kamal Foroughi, 78, who was also arrested for alleged espionage six years ago.
The oil and gas worker was jailed in 2013 for eight years but it only came to light two years ago when his family spoke out.
It is not clear what led to his arrest but he was given seven years in prison for spying and an extra year for having alcohol in his home.
Human rights experts have said that Iran’s police and secret services are very suspicious of dual nationals, especially if they are British or American.
The UN has said this has increased since 2015 when Barack Obama struck a nuclear deal, which President Trump now says they are violating.
Whitehall sources have also told The Sun that Theresa May upset Tehran when she was Home Secretary and detained two Iranian officials when they landed at Heathrow even though they had visas.
They were placed in an immigration detention centre and deported within a week.