Here is a timeline of the key events since Nazanin Zaghari-Ratcliffe was arrested in Iran in 2016.

– April 3 2016: The mother-of-one is detained by the Iranian Revolutionary Guard at Imam Khomeini airport after a holiday visit to Iran where she introduced her daughter Gabriella to her parents.

– July 12 2016: Richard Ratcliffe, her husband, delivers letters to Downing Street for outgoing prime minister David Cameron and his replacement Theresa May on his wife’s 100th day in custody. He says it is “astonishing” no British minister has publicly criticised Tehran for arresting Mrs Zaghari-Ratcliffe.

– August 9 2016: New prime minister Mrs May “raised concerns” about Mrs Zaghari-Ratcliffe during a phone call with president of Iran, Hassan Rouhani.

– September 9 2016: Mr Ratcliffe says his wife has been jailed for five years following a conviction on unspecified “national security-related” offences – a sentence he describes as “a punishment without a crime”.

– November 13 2016: Mrs Zaghari-Ratcliffe begins a hunger strike, which she ends after five days amid her family’s fears for her health.

– January 2 2017: Mr Ratcliffe says Mrs May and her ministers could have “publicly stood up for Nazanin more” and should have called for her release. Mr Ratcliffe said: “She raised those concerns in September. What happened after September? Nothing much, really.”

– April 24 2017: The family of Mrs Zaghari-Ratcliffe say she has lost the final stage of her appeal against the sentence.

– November 6 2017: It is feared Mrs Zaghari-Ratcliffe may face a further period of imprisonment because of remarks made by then-foreign secretary Boris Johnson. Mr Johnson told a parliamentary committee the previous week that Mrs Zaghari-Ratcliffe was working in Tehran training journalists at the time of her arrest in 2016. Four days later, she was summoned before an unscheduled court hearing, where the foreign secretary’s comments were cited as proof that she was engaged in “propaganda against the regime”.

– November 7 2017: It is announced that Mr Johnson told his Iranian counterpart in a phone call that his comments to a Commons committee provide “no justifiable basis” for further legal action against Mrs Zaghari-Ratcliffe. A Foreign Office spokesman says Mr Johnson now accepts that he “could have been clearer” when he told the Foreign Affairs Committee that the British woman had been training journalists in Iran at the time of her arrest.

– November 12 2017: Mr Ratcliffe says his wife has seen a medical specialist after finding lumps on her breasts and is “on the verge of a nervous breakdown”.

– November 15 2017: Mr Ratcliffe describes an hour-long meeting with Mr Johnson as “positive and constructive”.

– December 12 2017: Mr Johnson said he and his Iranian counterpart spoke “frankly” regarding the case of Mrs Zaghari-Ratcliffe, during talks in Tehran.

– Later in December 2017: Mr Ratcliffe said he believes there is “still a chance” his wife may be released in time for a dream Christmas together.

– December 28 2017: Mr Ratcliffe says he is in limbo waiting for news of his wife’s release but has not given up hope, and describes the situation as “a lot more positive” than last year.

– April 14 2018: Iranian ambassador to the UK, Hamid Baeidinejad, says the Iranian government is doing its best to secure Mrs Zaghari-Ratcliffe’s release, saying the judicial process was “complicated” but insisted “we are trying our best”.

– May 21 2018: Mr Ratcliffe says his wife has been told to expect another conviction after appearing in court over a new “invented” charge.

– August 3 2018: New foreign secretary Jeremy Hunt pledges to do everything possible to secure Mrs Zaghari-Ratcliffe’s release, after talks with Mr Ratcliffe.

– August 21 2018: Mr Hunt says he is considering a request by Mrs Zaghari-Ratcliffe’s husband to grant her diplomatic protection.

– August 23 2018: Mrs Zaghari-Ratcliffe is given temporary release from prison for three days and her husband says it feels like “home is one step closer”. She returns to prison three days later.

– September 26 2018: Mrs May and Mr Hunt ramp up pressure on Iran to release the charity worker during talks in New York. The PM tells Mr Rouhani she has “serious concerns” about the jailing of Mrs Zaghari-Ratcliffe.

– December 26, 2018: Mrs Zaghari-Ratcliffe turns 40 in jail. Three days later, she marks her 1,000th day of incarceration.

– January 14 2019: She begins a hunger strike in protest over her treatment in jail. The action ends after three days.

– January 24 2019: Iranian foreign minister Javad Zarif raises hope of Mrs Zaghari-Ratcliffe’s return to the UK by suggesting she could be freed in exchange for an Iranian woman held in Australia on a US extradition request. The minister subsequently backs away from his comments.

– June 15 2019: Mrs Zaghari-Ratcliffe begins another hunger strike, this time lasting 15 days. She is joined, in a show of solidarity, by her husband, who strikes outside the Iranian Embassy in London.

– June 24 2019: Mr Johnson, who came under fire as foreign secretary for his comments about Mrs Zaghari-Ratcliffe’s case in 2017, becomes Prime Minister. Dominic Raab replaces Mr Hunt as Foreign Secretary.

– September 23 2019: Mr Ratcliffe says Mr Johnson can make amends for his failings in his incarcerated wife’s case by telling Iran’s president “enough is enough” and securing her release.

– October 10 2019: The couple’s daughter, Gabriella, returns to the UK after more than three years living in the Middle East. The child, who is now five years old, had been living with her grandparents in Tehran since her mother was arrested. Her father says: “It has been a long journey to have her home, with bumps right until the end.”

– December 18 2019: Mr Ratcliffe is joined by Gabriella singing Christmas carols outside Downing Street, and he called on the Prime Minister to “please take responsibility for Nazanin’s case and do what you can to get her and others home”.

– January 3 2020: A US air strike kills Iran’s top military chief, General Quassem Soleimani. Mr Ratcliffe says he is worried about his wife, and tells ITV’s Good Morning Britain: “I sit here partly worried for what that means for Nazanin, partly worried what that means for my in-laws, sat in their ordinary living room in Tehran where they’re all really worried.”

– January 10 2020: Mrs Zaghari-Ratcliffe spends one night in a clinic after suffering “palpitations and panic attacks” due to the tensions in Tehran, sparked by the death of Gen Soleimani, Mr Ratcliffe says.

– January 23 2020: Mr Ratcliffe and their five-year-old daughter Gabriella meet the Prime Minister in Downing Street, but Mr Ratcliffe says there was “no breakthrough”.

He tells reporters: “I don’t think I have come away thinking Nazanin is coming out tomorrow or even next week, and I will think carefully about what I tell her on the phone on Saturday about where the hope is to come.”

– February 23 2020: Commons Leader Jacob Rees-Mogg tells the House: “It is a particular concern that the coronavirus has been rumoured – but I emphasise rumoured and not confirmed – to be in the prison in Evin where Mrs Zaghari-Ratcliffe is.”

– February 29 2020: Mr Ratcliffe says he believes his wife has contracted coronavirus in prison as he expresses concern at the jail’s “refusal to test her”.

– March 3 2020: The couple’s Labour MP, Tulip Siddiq, says she believes Mrs Zaghari-Ratcliffe may be temporarily released from jail due to the Covid-19 outbreak in Iran.

She tweets: “News from Iranian Ambassador that my constituent Nazanin Zaghari-Ratcliffe may be released on furlough today or tomorrow from prison in Iran.

“If this is true, Nazanin would welcome leaving Evin jail, but we’ve been here before.”

– March 17 2020: Mrs Zaghari-Ratcliffe is temporarily freed from jail. She says she is “happy to be out, even with the ankle tag” and can only go within 300 metres of her parents’ home.

– March 28 2020: Mrs Zaghari-Ratcliffe’s temporary prison release is extended to April 18 and Mr Ratcliffe says his wife’s file has been put forward to the Iranian prosecutor general to be considered for clemency.

– April 21 2020: After a delay, Mrs Zaghari-Ratcliffe’s prison release is extended again for around one month. Mr Ratcliffe, speaking on BBC Radio 5 Live, reveals that the family are able to talk via video calls for about four to five hours a day.

– May 20 2020: Mr Ratcliffe says his wife’s release has been extended indefinitely until there is a decision on her clemency. He describes the news as “a real step forwards… I don’t think it’s guaranteed one way and I don’t think she thinks it’s guaranteed one way, but let’s enjoy the moment.”

– May 26 2020: Mr Ratcliffe says the family are on the “cusp of potentially good news” and thinks the family could find out about a decision on her clemency the following day.

–August 24 2020: Lawyers for Mrs Zaghari-Ratcliffe ask Defence Secretary Ben Wallace for a meeting and call on the British Government to stand up to Iran over its “abusive treatment”.

– September 8 2020: Mrs Zaghari-Ratcliffe appears before a branch of Iran’s Revolutionary Court in Tehran, where she faces a new charge.

– March 7 2021: On the day Mrs Zaghari-Ratcliffe’s sentence is due to come to an end, her constituency MP Tulip Siddiq reveals she has had her electronic tag removed but faces a new court date.

Foreign Secretary Dominic Raab says her treatment is “intolerable” and calls on Iran to allow her to return to the UK.

– April 26 2021: Mrs Zaghari-Ratcliffe is given an additional one-year jail term and is also banned from leaving Iran for a year.

Her lawyer Hojjat Kermani says she received the second jail sentence on a charge of spreading “propaganda against the system” for participating in a protest in front of the Iranian Embassy in London in 2009.

Mr Johnson says the decision to sentence Mrs Zaghari-Ratcliffe to another year in prison is “cruel, inhumane and wholly unjustified”.

– May 2 2021: Dominic Raab admits Mrs Zaghari-Ratcliffe is effectively being held hostage by Iran, describing her treatment as torture.

Iranian state TV reports the UK will pay the £400 million debt to Iran to free Mrs Zaghari-Ratcliffe, citing an anonymous official.

Mr Ratcliffe says he and his family “have heard nothing” about his wife’s release.

But he adds it is “probably a good sign” such news is being reported in Iran, telling PA: “It’s probably a good sign that it’s being signalled, just as last week’s sentence was a bad sign.

“But it feels part of the negotiations rather than the end of them.”