UK authorities have given diplomatic protection to Nazanin Zaghari-Ratcliffe, the British-Iranian charity worker detained by Tehran.
It is an official recognition by the British government that Iran had not met its obligations under international rules in regard to her treatment and makes it a formal matter between the states.
Ms Zaghari-Ratcliffe was jailed for five years in September 2016 for supposedly planning to topple the Iranian government – charges she vehemently denies.
Her husband Richard Ratcliffe said it would leave Ms Zaghari-Ratcliffe, who went on a hunger strike in January angry at a lack of medical access, "a bit more upbeat". The decision recognised the treatment of her was an "outrageous violation," he added.
The British government said the legal proceedings brought against her “failed to meet international standards", and she was often denied medical care despite doctors' recommendations.
"Until yesterday, it was our problem that the British government was sympathetic with, in solidarity with, trying to help us along the way," Mr Ratcliffe told the BBC.
"Now it's also the British government's case and all the injustices that happen to Nazanin are effectively injustices to the British government."
Foreign minister Jeremy Hunt said the decision had not been made lightly, describing Ms Zaghari-Ratcliffe as an "innocent woman" separated from her daughter and husband.
“We have been working hard to secure her release but despite repeated efforts have not been successful. We have not even been able to secure her the medical treatment she urgently needs despite assurances to the contrary.”
“I have considered the unacceptable treatment Nazanin has received over three years, including not just lack of access to medical treatment but also lack of due process in the proceedings brought against her,” he said.
“My decision is an important diplomatic step that signals to Tehran that its behaviour is totally wrong.
"It is unlikely to be a magic wand that leads to an overnight result but it demonstrates to the whole world that Nazanin is innocent and the UK will not stand by when one of its citizens is treated so unjustly.”
