International sanctions had made it “extremely difficult” for <a href="https://www.thenationalnews.com/world/europe/iran-loses-latest-skirmish-over-ps400-million-arms-debt-1.978527" target="_blank">Britain to settle a £400 million ($542.8m) arms deal debt with Tehran</a>, a senior UK minister claimed on Thursday. Tulip Siddiq, the MP representing Nazanin Zaghari-Ratcliffe’s constituency in London, revealed an agreement collapsed last year that could have triggered the release of detained British citizens in Iran, one of whom is Ms Zaghari-Ratcliffe. Ms Siddiq told the UK Parliament that Britain had signed a deal with the regime last summer over the decades-old debt but it broke down, leaving at least four British passport holders stranded in Iran on trumped-up charges. Ben Wallace, the UK's Defence Secretary, told Times Radio that the main stumbling block was the UK had to uphold its obligations over the debt. “We also have international law obligations around sanctions and that makes how we hand back that money very difficult while Iran is in breach of all sorts of obligations, and indeed engaged in malign activity around the Middle East," he said Thursday. <a href="https://www.thenationalnews.com/world/europe/uk-foreign-secretary-dominic-raab-calls-for-prisoner-release-in-talks-with-iran-1.1113317">Former foreign secretary Dominic Raab </a>told families in August last year that the UK had come tantalisingly close to striking an agreement with Iran that would have secured the release of prisoners, but declined to give further details. Details of the failure in 2021 come amid rising hopes among the foreign prisoner population at Evin jail in Tehran that horse-trading during talks to re-establish the <a href="https://www.thenationalnews.com/world/europe/2021/12/09/last-chance-for-iran-to-return-to-nuclear-deal/" target="_blank">2015 nuclear agreement with the United States</a> could eventually lead to their freedom. Supporters of Ms Zaghari-Ratcliffe, 43, and <a href="https://www.thenationalnews.com/world/uk-news/2022/01/23/anoosheh-ashoori-british-national-jailed-in-iran-begins-hunger-strike/" target="_blank">Anoosheh Ashoori</a>, 67, a retired British-Iranian engineer sentenced to jail for a decade on charges of spying for Israel, say that settling the debt is a vital part of any deal to secure their release. Mr Wallace said London continued to seek a resolution even under the sanctions regime. "So we are trying to navigate a route through, we're trying to navigate that,” he added. The UK struck a deal with <a href="https://www.thenationalnews.com/world/europe/the-shah-era-deal-that-poisoned-relations-for-four-decades-1.933746" target="_blank">pre-Revolution Iran to sell 1,500 Chieftain tanks in the 1970s.</a> The UK received payment but the deal was cancelled after the overthrow of the Shah. The UK has been ordered by a specialist European commerce court to hand over the money but a legal battle has continued in London about the exact amount that should be paid, to the intense annoyance of the Iranians. The dispute has rumbled on for so long that it has become entangled in international sanctions imposed in 2008 on the Iranian military authority seeking the money. In 2014, before becoming defence secretary, Mr Wallace had described Britain’s role as “marred by double dealing and obfuscation”. Ms Zaghari-Ratcliffe, 43, a charity worker, has been held by Iran for nearly six years after being convicted on trumped-up espionage charges during a trip to visit her parents with her young daughter in April 2016. She has always denied the allegations and her supporters believe she and other dual citizen prisoners are being held as pawns in a larger diplomatic battle being played by Iran and the West. Speaking in Parliament Ms Siddiq said: “I understand the UK government signed an agreement with the Iranian authorities last summer that would have resulted in the payment of the £400m that we owe Iran and the release of my constituent, Nazanin Zaghari-Ratcliffe. "That agreement fell through and the debt still hasn't been paid. This case urgently needs the prime minister's attention and personal intervention.” Iran’s former senior international negotiator, Seyed Abbas Araghchi, claimed in August last year that the deal was blocked by the Americans. <a href="https://www.thenationalnews.com/mena/iran/2021/09/15/iran-replaces-nuclear-diplomat-in-foreign-ministry-reshuffle/" target="_blank">Mr Araghchi, who was replaced the following month, wrote on Twitter</a>: “You know better than anybody else that deal for release of 10 prisoners – incl Anoosheh Ashoori – was concluded weeks ago but your friends in [Washington} DC froze it.” Despite last year’s failure, Sherry Izadi, Mr Ashoori’s wife, said on Thursday that dual-citizen prisoners at Evin jail were “really, really hopeful” that the current international talks could lead to a breakthrough. “If this opportunity is lost, they will be there for a very long time. That prospect is very, very troubling,” she said. Mr Johnson on Wednesday agreed to meet Ms Zaghari-Ratcliffe’s husband, Richard, to discuss the case further. He said the debt was "difficult to settle and to square away for all sorts of reasons to do with sanctions, but we will continue to work on it". "No one has abandoned the efforts, it's just absolutely not as straightforward as people would think," he said. "There's a sense of urgency, we're trying to resolve this but it's difficult in the face of an Iran which is effectively taking hostages."