The British foreign secretary, Boris Johnson, said the UK would appeal to Iran on humanitarian grounds to free a jailed aid worker but expressed reservations that granting her diplomatic protection would help secure her release, her husband said on Wednesday.

Nazanin Zaghari-Ratcliffe, a project manager with the Thomson Reuters Foundation, was sentenced to five years in prison after being convicted by an Iranian court of plotting to overthrow the clerical establishment. She denies the charges.

Mr Johnson came under pressure to resign after comments he made earlier this month that Ms Zaghari-Ratcliffe, who has dual nationality, had been training journalists before her arrest, in April 2016. Critics said the comments might have prompted Iran to extend her sentence, and he apologised for his remarks on Monday.

On Wednesday Mr Johnson met her husband, Richard Ratcliffe, and told him the UK would leave no stone unturned in its bid to free her, saying the British ambassador in Tehran had earlier raised her case again with the Iranian authorities.

Mr Johnson also stressed the importance of an appeal on humanitarian grounds, Mr Ratcliffe told reporters, saying it had been a positive meeting.

But officials had questioned whether it would help to grant his wife diplomatic protection, a move that would explicitly make Ms Zaghari-Ratcliffe’s fate an issue in state-to-state relations rather than a purely consular case.

Denied fair trial

A legal opinion prepared for the human-rights charity Redress on Ms Zaghari-Ratcliffe’s case said the British government could grant her diplomatic protection as she is “predominantly” a British citizen who has been denied a fair trial.

“I said I thought it would be important and helpful . . . The foreign secretary and the foreign office expressed reservations,” Mr Ratcliffe said. The foreign office said lawyers would meet in the next fortnight to discuss the issue further.

Nazanin Zaghari-Ratcliffe: Foreign Secretary Boris Johnson with Richard Ratcliffe at the Foreign Office in London. Photograph: Stefan Rousseau/PA Wire

Iran’s state news agency, Irna, also signalled that such a move could backfire, citing comments by an unidentified international-law expert. “In Iran’s view, Zaghari is an Iranian citizen, and was tried, due to her illegal actions, and convicted in Iranian courts; and now she is serving her sentence,” it quoted the expert as saying.

“Hence the UK’s interference, other than through peaceful paths and humanitarian issues, is considered an intervention in Iran, and will (naturally) trigger Iran’s severe reaction.”

Mr Ratcliffe said Mr Johnson was keen to take him on a trip to Iran planned before the end of the year, which could allow him to see his wife and three-year-old daughter, who is being cared for by relatives in Iran, for the first time in 19 months.

“For me it’s very important to be going on that trip, to be standing alongside the foreign secretary, and I understand that’s a big ask. It’s reasonably unprecedented, but I think it’s important in our circumstances,” he said.

Mr Ratcliffe, who said his wife appeared to be on the edge of a nervous breakdown, and was due to have further tests after finding lumps on her breasts, said he thought she was being used as a diplomatic bargaining chip.

“There are fights that are nothing to do with us . . . We’re being used as a vehicle for those fights,” he said. – Reuters