Boris Johnson is set to meet with Richard Ratcliffe, the husband of a British woman jailed in Iran, Nazanin Zaghari-Ratcliffe.
Iran is poised to reject a United Kingdom proposition to grant Nazanin Zaghari-Ratcliffe diplomatic protection, a move advocated by her family to escalate her case from a consular issue to a state matter.
She has been in Tehran's notorious Evin Prison since then and her husband has accused Mr Johnson of possibly increasing her sentence by five years after he told MPs last week she was "teaching people journalism" in the country.
On Mr Ratcliffe's request to accompany Mr Johnson to Iran before the end of the year, the spokesman said: "Our overriding principle in handling this case is to secure a permanent family reunion, not a temporary one".
Image: Nazanin Zaghari-Ratcliffe, husband Richard Ratcliffe and their child.
He will speak to the Foreign Secretary at the Foreign Office at 10am, in a bid to help secure his wife's release from Iran.
"The Government will continue to do this in the way that we judge is in their best interests and the Foreign Secretary has made it clear that no stone should be left unturned".
Iran's response to diplomatic protection came in the form of an interview with an anonymous global law expert from Iran, but the gravity of the matter indicates it also reflected the official view.
Also at the meeting in the Foreign and Commonwealth Office in London was Middle East minister Alistair Burt, who has met Mr Ratcliffe before and visited Mrs Zaghari-Ratcliffe's family in Tehran, and FCO consular officials who have been providing support to the family. She is staying with her grandparents in Tehran.
"She was on the news in Iran again on Saturday night; the broadcaster repeated the argument that you had "revealed" Nazanin's so-called crimes".
Mr Ratcliffe added: "My wife is angry now".
"She cried over the coverage and felt it was a violation that they used pictures from our family photo album".
"She talks about being on the verge of a nervous breakdown".
"The stress is taking a physical toll on her".
Ratcliffe went on to say that he was becoming "exponentially" concerned about his wife's health, especially given that she had discovered lumps in her breast.
"Nazanin is being held because she is British and is being used as a bargaining chip against the United Kingdom, now justified by your words", he said in an article in the Evening Standard newspaper.
"It's very important for me to go on that trip, to be standing alongside the Foreign Secretary, and I understand that's a big ask, it's reasonably unprecedented, but it's important for me".
The seriousness of Johnson's error became apparent days later when Zaghari-Ratcliffe was summoned to an unscheduled court hearing at which the Foreign Secretary's remarks were cited as proof that she had engaged in "propaganda against the regime".
A spokesman said: "The Foreign Secretary and officials outlined that the key question is whether diplomatic protection will have a positive impact on the case, given all the representations that have already been made. I can not give her an answer today; I would rather answer Mr Ratcliffe in person".
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