Media playback is unsupported on your device Media caption Nazanin Zaghari-Ratcliffe's daughter, Gabriella, cuts her own "welcome home" cake with help from her dad, Richard

The five-year-old daughter of a British-Iranian woman jailed in Iran on spying charges has returned to the UK.

Nazanin Zaghari-Ratcliffe, 40, a charity worker from London, has been detained for three years over the allegations, which she denies.

Her British-born daughter Gabriella, who has been living with her grandparents in Tehran, returned on Thursday to start school in the UK.

Gabriella's father, Richard Ratcliffe, said she has been "so brave".

Appearing with Gabriella at a news conference at the Houses of Parliament, Mr Ratcliffe said she struggled speaking English but had been keen to tell him that she wanted to visit a toy shop.

He said she "told mum that she'll see her back in London".

"She's promised mummy she's going to be brave. It's just lovely to hold her again."

Image copyright PA Media Image caption Richard Ratcliffe embraces his daughter, Gabriella, after she landed back in the UK

Image copyright PA Media Image caption Gabriella brought a cake into a news conference at the Houses of Parliament on Friday afternoon

Nazanin Zaghari-Ratcliffe was arrested in April 2016 during a visit to introduce Gabriella to relatives, her family said. She is now being held in Tehran's Evin prison, where Gabriella visited her at least once a week.

But in April the family said new prison rules meant Mrs Zaghari-Ratcliffe could only see her daughter once a month and that she was banned from making international calls.

Earlier this month Mrs Zaghari-Ratcliffe wrote an open letter to mothers of Iran, in which she said: "In the near future, my baby will leave me to go to her father and start school in the UK. It will be a daunting trip for her travelling, and for me left behind."

Last week, Mr Ratcliffe from West Hampstead, told the Times that they had agreed Gabriella should return to the UK for the start of the school year in September, but postponed the decision after Mrs Zaghari-Ratcliffe was taken to a psychiatric hospital.

"I spoke to Nazanin yesterday and she was reasonably distraught," he told reporters at Westminster on Friday.

"One of the things she really didn't want to happen was her daughter to leave while she was still in prison."

Mr Ratcliffe said there is a "real risk" his wife's mental and physical condition will deteriorate.

Image copyright PA Media Image caption Richard and Nazanin agreed that Gabriella should return to the UK to begin school, the family said

In response to Gabriella's return, Foreign Secretary Dominic Raab reiterated his earlier calls for Iran to release Mrs Zaghari-Ratcliffe and said the family's situation was one that no parent "should ever have to face".

"Gabriella is an innocent child and should be able to go to school and be with both her parents," he said. "We continue to urge Iran to release Nazanin immediately so the family can be reunited in the UK."

His predecessor, Jeremy Hunt, described the news of Gabriella's homecoming as "the definition of bittersweet".

He called on the British government to "redouble" its efforts to secure Mrs Zaghari-Ratcliffe's release, tweeting: "Now more than ever, she needs to know she's not alone."

Image copyright AFP PHOTO / FREE NAZANIN CAMPAIGN Image caption Mrs Zaghari-Ratcliffe was temporarily reunited with her daughter Gabriella during a three-day release from prison in August last year

Mr Ratcliffe told reporters that his wife had shared a prison cell with British-Australian woman Jolie King, who had been detained with her boyfriend in Tehran earlier this year for reportedly flying a drone without a permit.

Ms King and her boyfriend, Mark Firkin, were released last week.

Iran has detained a number of dual citizens and foreign nationals in recent years, many of them on spying charges. The exact numbers are not known.

The arrests and a row over the seizure of oil tankers in the Gulf. have led to increasingly tense diplomatic relations between the UK and Iran.

Iran also claims it is owed £400m by the UK in relation to contracts signed more than 40 years ago between the International Military Services (IMS) - a company that has ceased trading but was used by the Ministry of Defence to sell defence equipment - and the pre-Islamic Revolution Iranian regime.

The contracts involved the supply of tanks to Iran, which were paid for but undelivered in the wake of the country's 1979 revolution.

Litigation regarding the dispute is under way.

The UK government said it does not "share the view" that the IMS debt, or any other bilateral issue, is the reason for Mrs Zaghari-Ratcliffe's detention, and that the two issues are "entirely separate".

"Iran must live up to its responsibilities under international human rights law and under the Vienna convention on consular relations, and release Nazanin, and the other dual national cases, without delay," a government statement issued by the Foreign Office said.

The family's MP, Tulip Siddiq, said Mrs Zaghari-Ratcliffe wants to know why the UK government is not doing more to secure her release.

Media playback is unsupported on your device Media caption Why one mother's personal plight is part of a complicated history between Iran and the UK (video published August 2019)

"I have now dealt with three prime ministers, with three foreign secretaries, with four Middle East ministers about this case," she said.

"Every single one of those politicians have looked me in the eye and said that this has nothing to do with the debt that we owe Iran. But we know that's not true."

Last month, Prime Minister Boris Johnson called for the release of Mrs Zaghari-Ratcliffe during a meeting with Iran's president.

In 2017, when he was foreign secretary, Mr Johnson had to apologise after saying Mrs Zaghari-Ratcliffe was in Iran "teaching people journalism" - despite her family's insistence she was there on holiday.