UK officials have downplayed the prospect of Nazanin Zaghari-Ratcliffe’s imminent release from Iran after state TV suggested Britain would pay a £400 million debt to secure her release.

Richard Ratcliffe, the husband of the British-Iranian charity worker, said the family had not been updated but welcomed the signals from Tehran over the long-running dispute as “a good sign”.

The Foreign Office said “legal discussions are ongoing” over the debt despite the claim made on Iranian state TV, which cited an anonymous official.

It was said that the UK Government’s position had not changed over the weekend and that Iran had made the claim before without the mother of one being released.

Mr Ratcliffe, who has campaigned for the release of his wife after her detention in 2016, told the PA news agency: “We haven’t heard anything.

“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.”

Earlier in the day, Foreign Secretary Dominic Raab said the debt “is not actually the thing that is holding us up at the moment”.

The dispute dates back to the 1970s when the then-shah of Iran paid the UK £400 million for 1,500 Chieftain tanks.

Britain refused to deliver the tanks to the new Islamic Republic when the shah was toppled in 1979, but kept the cash despite British courts accepting it should be repaid.

Hopes were raised when Iranian state TV reported that the UK had agreed to pay the £400 million to see the release of the 42-year-old.

The anonymous official was also quoted saying a deal had been made between the US and Tehran for a prisoner swap in exchange for the release of seven billion dollars (£5 billion) of frozen Iranian funds.

But Washington denied the report, saying suggestions of a prisoner swap were “not true”.

A Foreign Office spokesman said: “We continue to explore options to resolve this 40-year-old case and will not comment further as legal discussions are ongoing.”

Speaking to the BBC on Sunday morning, Mr Raab said the debt was not the issue holding up Mrs Zaghari-Ratcliffe’s release.

He cited elections in Iran as being key, as well as the Iran nuclear deal officially titled the Joint Comprehensive Plan of Action (JCPoA).

“That is not actually the thing that’s holding us up at the moment, it’s the wider context as we come up to the Iranian presidential elections and the wider elections on the JCPoA which inevitably, from the Iranian perspective, the two are considered in tandem,” he told The Andrew Marr Show.

Mr Raab said it was clear the Iranians were using Mrs Zaghari-Ratcliffe as “leverage” and suggested authorities were holding her “hostage” in treatment amounting to “torture”.

The report in Iran raised the prospect that there was co-ordinated action between Tehran, London and Washington.

Last Monday, Prime Minister Boris Johnson acknowledged “we are working with our American friends on this issue”.

Mrs Zaghari-Ratcliffe, of north London, was detained in Tehran in 2016 while taking daughter Gabriella to see her family, as authorities made widely refuted allegations of spying.

She completed a five-year sentence in March, having carried out hunger strikes in protest over her treatment in jail as diplomatic efforts were made to secure her freedom.

But she and her family were delivered a fresh blow last week when she was given an additional one-year jail term. She was also banned from leaving Iran for a further year.

Labour MP Tulip Siddiq, who represents Mrs Zaghari-Ratcliffe’s constituency of Hampstead and Kilburn, spoke of the shock the family felt on hearing the development in Tehran, as she called for the debt to be resolved now they are at “the final hurdle”.

“Nazanin’s family has been burned before which is why they’re not celebrating quite yet, but it came as an utter surprise,” she told PA.

Ms Siddiq said the British ambassador to Tehran visited Mrs Zaghari-Ratcliffe on Sunday morning at her parents’ home, where she is awaiting her sentence while appealing the verdict.

“They talked about various things, including coronavirus and the spread in Evin prison and whether she qualifies for a vaccine,” Ms Siddiq said.

“But there was no mention whatsoever of this news that broke through Iranian media.”