West Hampstead mum Nazanin Zaghari-Ratcliffe has had her passport returned and a British negotiating team is in Tehran, her MP has said.

Nazanin has been detained in Iran since her arrest in 2016 on charges of plotting to overthrow the government – allegations she has always denied.

Hampstead and Kilburn MP Tulip Siddiq tweeted on Tuesday that her British passport has been returned.

But asked about the case, the Prime Minister said: “I don’t want to tempt fate”.

“Negotiations about all our difficult consular cases have been going on for a long time,” he told reporters, saying “quite delicate discussions” are still taking place.

A £400 million debt relating to a cancelled order for 1,500 Chieftain tanks dating back to the 1970s had been linked to the continued detention of Nazanin and other UK-Iranian dual nationals.

In December, Foreign Secretary Liz Truss said the £400 million that Britain owes Iran is a “legitimate debt” that the Government wants to pay.

On Tuesday, a No 10 official said of the debt: “There is no change on our position to that.

“We are committed to paying the debt. We’re exploring options to resolve it – it has not been resolved.”

Pressed on whether a UK negotiating team is in Tehran, he added: “I’m not going to get into further speculation at this point.”

Mr Johnson was also reluctant to say too much, telling reporters: “I think that it’s very important when you have got quite delicate discussions going on, negotiations going on in Tehran about some of our most difficult consular cases – particularly Nazanin Zaghari-Ratcliffe – you should say as little as possible unless and until the thing is actually concluded.

“Everybody wants Nazanin home, we have been working on that for a long, long time. I do not want to do anything to interrupt the conversations right now.”

On Tuesday, Ms Siddiq tweeted: “I am very pleased to say that Nazanin Zaghari-Ratcliffe has been given her British passport back. She is still at her family home in Tehran. I also understand that there is a British negotiating team in Tehran right now. I will keep posting updates as I get them.”

Ham & High: Nazanin Zaghari-RatcliffeNazanin Zaghari-Ratcliffe (Image: PA Media)

According to her employer, the Thomson Reuters Foundation, her lawyer Hojjat Kermani, when asked whether Mrs Zaghari-Ratcliffe will be released, said: “I am hopeful that we will have good news soon.”

Nazanin was arrested in Iran as she prepared to fly back to the UK, having taken her daughter Gabriella – then not yet two years old – to see relatives.

She was accused of plotting to overthrow the Iranian government and sentenced to five years in jail, spending four years in Tehran’s Evin Prison and one under house arrest.

Her husband, Richard Ratcliffe, spent 21 days on hunger strike last year in London to draw attention to his wife’s case.

In January, the daughter of another British-Iranian detained in Iran said her father was to begin a hunger strike due to a lack of progress in securing his release.

Retired civil engineer Anoosheh Ashoori has been held at Evin Prison on charges of spying for Israel, which he denies, for more than four years.

In a video posted in relation to the hunger strike, Elika Ashoori said she was at that time “extremely concerned” for her father’s health “as he approaches his 68th birthday”.

In December, Foreign Secretary Liz Truss said the £400 million that Britain owes Iran is a “legitimate debt” that the Government wants to pay.

Sacha Deshmukh, Amnesty International UK’s chief executive, warned that the latest reports should be treated with caution as there had been “false dawn after false dawn” in the long-running process.

He said: “We sincerely hope these reports are correct.

“The detainees and their families have been suffering for years, and a resolution can’t come quickly enough.

“It’s been clear for a long time that the Iranian authorities have been targeting foreign nationals with spurious national security-related charges to exert diplomatic pressure.

“In the past we’ve had false dawn after false dawn over possible breakthroughs, so it’s only right to be cautious at the moment.”

In relation to the debt, the Foreign, Commonwealth and Development Office said: “We continue to explore options to resolve this case and will not comment further as discussions are ongoing.”

On the cases of Britons detained, a Foreign Office spokesperson said: “We have long called for the release of unfairly detained British nationals in Iran. We don’t comment on speculation.”