Held at Evin prison in Tehran, Ms Zaghari-Ratcliffe and fellow inmate Narges Mohammadi will refuse all food for 72 hours after the former was denied medical care, officials rejecting her request for a doctor to examine lumps on her breasts and treat neck pain and numbness in her arms and legs.

Husband Richard Ratcliffe has called for an urgent meeting with the Iranian ambassador to London.

Iran sentenced Ms Zaghari-Ratcliffe to five years in prison in September 2016 after accusing her of “plotting to topple the Iranian regime”.

A project manager for the Thomson Reuters Foundation, the charitable arm of the Reuters news agency, she had visited the country to spend time with family members for Nowruz (New Year) on 17 March 2016 but was detained on her way home to the UK at Imam Khomeini Airport on 3 April.

Her 22-month-old daughter, Gabriella, was left to the care of her maternal grandparents, resident in Iran.

Ms Zaghari-Ratcliffe stands accused of running “a BBC Persian online journalism course which was aimed at recruiting and training people to spread propaganda against Iran”, according to the country’s prosecutor-general, speaking in Tehran in October 2017.

The allegation relates to her previous role working for the BBC World Service Trust, now rechristened BBC Media Action, between February 2009 and October 2010, contributing to a course undertaken by several employees of an Iran technology news website, for which they were subsequently imprisoned.

The BBC has denied the charge and said her imprisonment was based on a false premise anyway, as her role within the organisation had been that of a junior administrative assistant.

The Iranian government has never disclosed the precise nature of the crimes Ms Zaghari-Ratcliffe is thought to have committed, although it insists she has been detained on legitimate grounds.

Richard Ratcliffe has sought to raise awareness of her plight from Britain, launching an online petition calling on prime minister Theresa May and Iran’s supreme leader Ali Khamenei to free her.

“Nazanin is not being held for anything she has personally done. It is deeply misleading by both governments to suggest or even half imply otherwise,” he has said.

“We demand a clear statement from the foreign secretary to correct his mistake – in parliament and in Tehran at the earliest opportunity.”

Nazanin Zaghari-Ratcliffe – in pictures Show all 20 1 /20 Nazanin Zaghari-Ratcliffe – in pictures Nazanin Zaghari-Ratcliffe – in pictures 2018 Nazanin Zaghari-Ratcliffe hugs her daughter Gabriella, in Iran after she was allowed to leave the Iranian prison, she is being held in, for three days. Zaghari-Ratcliffe was arrested during a holiday with her toddler daughter in April 2016. Iranian authorities accuse her of plotting against the government. Her family denies this, saying says she was in Iran to visit family. Free Nazanin Campaign/AP Nazanin Zaghari-Ratcliffe – in pictures Nazanin Zaghari-Ratcliffe with her husband Richard Ratcliffe and their daughter Gabriella. Nazanin is serving a five-year prison sentence for allegedly plotting to overthrow Iran's government. PA Nazanin Zaghari-Ratcliffe – in pictures June 2016 Richard Ratcliffe's daughter Gabriella had her British passport confiscated and was stranded in Iran with her grandparents after her mother Nazanin was jailed. He left left a giant birthday card on the doorstep of the Iranian embassy in central London to mark her second birthday in June 2016. PA Nazanin Zaghari-Ratcliffe – in pictures Nazanin has spent some of her prison sentence in solitary confinement. PA Nazanin Zaghari-Ratcliffe – in pictures Nazanin Zaghari-Ratcliffe with her husband Richard and daughter Gabriella. Family Handout Nazanin Zaghari-Ratcliffe – in pictures July 2016 Richard Ratcliffe delivering a letter of petition with his mother Barbara Ratcliffe and MP Tulip Siddiq, to 10, Downing Street on the 100th day of her detention, on July 12, 2016. Getty Nazanin Zaghari-Ratcliffe – in pictures Supporters of Nazanin Zaghari-Ratcliffe held a vigil outside the Foreign and Commonwealth Office to mark her 707 days in captivity. Getty Nazanin Zaghari-Ratcliffe – in pictures January 2017 Richard Ratcliffe holds a '#Free Nazanin' sign and candle during a vigil for for wife on January 16, 2017. The vigil, being held outside the Iranian Embassy in London marks one year since the Washington Post journalist Jason Rezaian and other US-Iranian dual-nationals were released from prison in Iran. Getty Nazanin Zaghari-Ratcliffe – in pictures Nazanin with her daughter Gabriella before they were detained by Iranian authorities. Change.org Nazanin Zaghari-Ratcliffe – in pictures September 2017 Gabriella, who is three-years-old in this picture, has now spent two years away from her mother. Richard Ratcliffe Nazanin Zaghari-Ratcliffe – in pictures November 2017 Foreign Secretary Boris Johnson meets with Richard Ratcliffe over Nazanin's case. They meet just days after Johnson told a parliamentary committee that she was in Iran "training journalists". WPA Pool/Getty Nazanin Zaghari-Ratcliffe – in pictures November 2017 Actor Emma Thompson braved pneumonia to support Richard Ratcliffe in leading demonstrators before a march in support of Nazanin in November. Reuters Nazanin Zaghari-Ratcliffe – in pictures November 2017 Richard Ratcliffe after the march said: 'It is profoundly moving to see so many people here.' REUTERS Nazanin Zaghari-Ratcliffe – in pictures November 2017 A picture of Nazanin Zaghari-Ratcliffe shown on Iranian state TV as part of a report that made fresh allegations against her. They said she had been recruiting for banned broadcast services, as well as 'opposition cyber teams'. Nazanin Zaghari-Ratcliffe – in pictures December 2017 Iranian president Hassan Rouhani greets British Foreign Secretary Boris Johnson at the presidential office in Tehran, Iran. Johnson visited Tehran to discuss the fate of detained Nazanin Zaghari-Ratcliffe. EPA Nazanin Zaghari-Ratcliffe – in pictures Nazanin Zaghari-Ratcliffe with her daughter Gabriella. PA Nazanin Zaghari-Ratcliffe – in pictures December 2017 Photos of Richard Ratcliffe and his wife Nazanin Zaghari-Ratcliffe on display at their home in north London. Mr Ratcliffe said he believed there was "still a chance" she may be released from an Iranian prison in time for a dream Christmas together. Unfortunately that didn't happen. PA Nazanin Zaghari-Ratcliffe – in pictures February 2018 Richard Ratcliffe delivers a petition and a letter addressed to the Iranian Deputy Foreign Minister Abbas Araghchi to demand her release, at the Iranian Embassy in London on February 21, 2018. He also left support letters for his spouse in the country's embassy, amid a visit by a deputy foreign minister. AFP/Getty Nazanin Zaghari-Ratcliffe – in pictures August 2018 Foreign Secretary, Jeremy Hunt meeting Richard Ratcliffe. Hunt has pledged to do everything possible to secure the release of a charity worker jailed in Iran Jeremy Hunt/PA Nazanin Zaghari-Ratcliffe – in pictures August 2018 Nazanin Zaghari-Ratcliffe hugs her daughter Gabriella, in Iran after she was allowed to leave the Iranian prison, she is being held in, for three days. Zaghari-Ratcliffe was arrested during a holiday with her toddler daughter in April 2016. Iranian authorities accuse her of plotting against the government. Her family denies this, saying says she was in Iran to visit family. PA

What he got instead was a highly unhelpful intervention from then-foreign secretary Boris Johnson, who was was widely criticised for muddying the waters.

“When I look at what Nazanin Zaghari-Ratcliffe was doing, she was simply teaching people journalism, as I understand it,” Mr Johnson told a foreign affairs committee on 1 November 2017.

“Neither Nazanin Zaghari-Ratcliffe nor her family has been informed about what crime she has actually committed. And that I find extraordinary, incredible.”

The careless statement that she was “teaching people journalism” reinforced the Islamic Republic’s stance and was roundly criticised by the likes of Labour leader Jeremy Corbyn and London mayor Sadiq Khan, and led to calls for Mr Johnson to resign.

Mr Johnson has since been replaced as foreign secretary while Mr Ratcliffe has alleged that his wife’s freedom hinges on the interest rate accumulated on a £450m loan the UK still owes Tehran over a cancelled arms deal in the 1970s, a charge the Foreign Office has vehemently denied.

He has also regularly raised concerns about her welfare in prison, amid concerns she could suffer a nervous breakdown and might have been tortured.

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In April 2018, a charity comedy night was staged to raise funds to support the campaign for her release, hosted by Shappi Khorsandi and featuring Al Murray, Mark Steel and Sara Pascoe.

In August, Ms Zaghari-Ratcliffe was taken to a prison clinic after suffering a panic attack just days after being temporarily released to see her family.