The husband of a West Hampstead mother who has been held in solitary confinement in an Iranian jail for five weeks has launched a desperate appeal for her return.

Nazanin Zaghari-Ratcliffe, 37, from West Hampstead, was seized by security services at Tehran’s main airport with her 22-month-old daughter as they were returning to the UK after visiting relatives on April 3.

Husband Richard Ratcliffe, 41, says daughter Gabriella has had her British passport confiscated and is stranded in Iran with her grandparents.

Charity worker Nazanin, an active member of the Hampstead Mums Facebook group, has been transferred to an unknown location in the Kerman province, south of Tehran, and is being held in solitary confinement.

Accountant Mr Ratcliffe has started a petition, which has 54,200 signatures, calling on Prime Minister David Cameron to intervene to bring his wife and baby daughter home.

He said: “Nazanin has not been allowed to access a lawyer or her daughter. She has not been able to call out of the country to speak to me, her British husband, and the Red Cross have not been able to make contact. There have been no charges.”

Nazanin has told her family she was forced to sign a confession. They are unaware of its content, but have been told the investigation relates to an issue of national security.

Mr Ratcliffe said: “It is hard to understand how a young mother and her small child on holiday could be considered an issue of national security. She has been to Iran to visit her family regularly since making Britain her home.”

He spoke to his wife’s family last night and said they are hopeful that her parents and Gabriella will be allowed to visit Nazanin on Wednesday.

He said: “They are flying down to Kerman in hope that this promise is kept.It may not be. But even one family visit after 37 days would mean the world. So please keep us in your prayers - and thank you all for publicising her case, and the effect this is having.”

Nazanin works as a project manager for the Thomson Reuters Foundation, based in Canary Wharf, which delivers charitable projects around the world but does not work in Iran.

Fellow Hampstead mum Diane von R, of the Hampstead Mums Facebook group, said: “Nazanin is a West Hampstead mum and she’s a fairly active member of the group. It was such a shock to see her in the news and I have been in touch with her husband Richard.”

Monique villa, Ceo of the Thomson Reuters Foundation, said the charity had no projects in Iran.

She said: “Nazanin had travelled to Tehran in a private capacity. We are in close contact with her family. We cannot understand the reason for her detention and hope the matter will be resolved as soon as possible”.