Sir Richard Dalton warned that there shouldn’t be “excessively high expectations” over what the foreign secretary can achieve on his trip to Iran later this year.
“The Iranians are already discounting the connection between Mrs Zaghari-Ratcliffe and the visit by saying that it was long planned.
“There are other things to discuss with Iran and it’s not clear just what Mr Johnson could bring to Iran that would help persuade them that it’s in Iran’s interest to release her,” Dalton told BBC Radio 4′s Today programme on Tuesday.
Downing Street has said it is considering giving Zaghari-Ratcliffe diplomatic protection in order to speed up her release from jail, but Dalton was unsure whether this tactic would work.
Dalton added: “I think this is going to be a long haul. I think it’s time to let the government get on with it and the less debate about political ramification in the UK from now on, the better. I don’t think there should be excessively high expectations.
“I think that the fact that there are several British cases that Mr Johnson quite rightly has to handle means that we shouldn’t expect too much from an early visit. ”
On Monday, Johnson finally admitted that it was “wrong” of him to claim that Zaghari-Ratcliffe was in Iran to train journalists, apologising if he caused “any further anguish”.
The senior Tory minister said that he will travel to Iran later this year “to review the full state of our bilateral relations and to drive home the strength of feeling in this house (Commons) and in the country at large about the plight of Mrs Zaghari-Ratcliffe and other consular cases”.
Johnson has faced calls to resign form all sides after he said that the British mother was in Iran training journalists. Her family said she was in Iran to visit family.
Zaghari-Ratcliffe was given a five-year sentence on allegations of spying.
Carla Ferstman, director of Redress, a human rights organisation specialising in torture, urged the government to act quickly to return Zaghari-Ratcliffe home.
Addressing the question of dual citizenship, and the challenges this can bring in some cases, Ferstman said: “There are a number of people, not only Britons, but from other nationalities around the world in Iran, this is a huge problem and it’s important that governments work together to solve it, to ensure that these individuals are not kept like hostages in Iran, used as political pawns.”
Speaking about the attention the case has got recently, Ferstman said: “One of the things that it (the publicity) has helped is to encourage the UK government to take this matter seriously.
“This is something that the family has been waiting for for a very long time, that their case is top priority of the government.
“And it’s really important from that perspective that the government acts now and acts quickly to take her home.”