Attempts to free a West Hampstead mum detained in Iran were frustrated after an agreement to settle a historic £400 million debt collapsed, MPs have heard.

The outstanding payment from Britain to Iran – relating to a cancelled order for 1,500 Chieftain tanks dating back to the 1970s – has been linked to the continued detention of Nazanin Zaghari-Ratcliffe and other UK-Iranian dual nationals held in the country.

Hampstead and Kilburn MP Tulip Siddiq told Prime Minister's Questions (PMQs) on Wednesday (February 9) that she understands an agreement over the debt was reached last summer but then fell through.

Boris Johnson responded that the government "remains committed" to securing Nazanin's release, adding: “She knows the IMS (International Military Services) debt is difficult to settle and to square away for all sorts of reasons to do with sanctions, but we will continue to work on it."

Richard said: “I have mixed feelings about today’s acknowledgment by the PM that there was an agreement with Iran last summer which then fell apart.

"I’m glad that negotiations continue – but again it feels like needless suffering.

"As the years pass, it does feel increasingly that the government has not just missed one opportunity to solve Nazanin’s case, but a series of them.

"The reasons behind the recurring decisions to obstruct remain opaque, but the negative fallout for us has been very clear.

"Six years of abuse is a long time to be living under jeopardy. We look forward to talking it all through with the PM when we meet."

Asked about Nazanin's welfare, he told the Ham&High: "She is up and down – watching closely what happens at the negotiations in Vienna (Iran nuclear talks), checking what gets reported on the news, hoping that this time we’ll be lucky, and fearing what will happen next if we’re not."

Ms Siddiq urged prime minister Boris Johnson to personally intervene in the matter, not any other minister.

Charity worker Nazanin was arrested at Tehran’s Imam Khomeini airport in April 2016 and sentenced to five years in jail after being accused of spying.

Last April she was given a further sentence of a year. The charges against her have always been widely disputed – a charge she vehemently denies.

Nazanin has yet to be allowed to return to the UK.

Mr Johnson said he could "have another meeting with Richard Ratcliffe in due course".

Also during PMQs, Newport West's Labour MP Ruth Jones said: “I understand the prime minister has been heard singing I Will Survive in recent days. I would suggest that he would be better off singing Careless Whisper instead, because, in 2017, Nazanin Zaghari-Ratcliffe was condemned to an extended prison sentence in Iran because of the careless words of this Prime Minister.

“Now, in 2022, this week, my friend, the leader of the opposition (Sir Keir Starmer) was hounded by thugs outside this Parliament because of the careless, disgraceful words of this Prime Minister.

“So will the prime minister do the decent thing? Will he reconsider his words, repent and resign?”

Mr Johnson replied: “I don’t think she should either let the thugs and yobs who bullied and harassed the right honourable gentleman off the hook, because they are culpable, any more than she should let the Iranian government off the hook, because they are culpable.”

Richard told the Ham&High: "Ruth Jones is my sister’s MP, and she came down to meet us both during my hunger strike last autumn.

"I asked my sister to pass on our thanks to Ruth for reminding the PM of his special responsibility in Nazanin’s case."