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.

Ratcliffe, who has campaigned for the release of his wife after her detention in 2016, said: “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.”

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 £400m for 1500 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 £400m 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 (£5bn) of frozen Iranian funds.

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

A Foreign Office spokesperson 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 yesterday, Raab said the debt was not the issue holding up 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.

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

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