The UK must appoint a special envoy to resolve a 40-year arms debt and secure the release of a Briton who this week exposed the chaos inside Tehran’s Evin jail during the coronavirus pandemic, his MP said on Friday. Janet Daby, whose constituent Anoosheh Ashoori revealed the lack of medicines for inmates, said that Iran must also end its destabilising role in the Middle East to allow for a deal on the Shah-era debt to be struck. The families of Mr Ashoori, 66, and Nazanin Zaghari-Ratcliffe, both British dual nationals, have cited Britain’s failure to settle payment for an aborted 1970s arms deal as a key reason why they remain held on trumped-up national security charges. A deal for more than 1,700 tanks and armoured vehicles agreed with the former Shah of Iran was aborted following the 1979 revolution and before the vehicles were delivered. Britain accepts that it owes money to Iran but claims it cannot legally hand it over because of 2008 European sanctions that were imposed on Iran’s defence ministry before the final bill was settled. Attempts to resolve the debt have been blocked by continuing legal action in the UK’s courts and disputes between British government departments, said the MP. Ms Daby, a member of the opposition Labour party, said that the failings had led to more British citizens suffering in Iranian prisons. Mr Ashoori’s family backed the MP and said that the dispute over the arms deal could be overcome by an independent envoy. The issue is likely to be discussed by a parliamentary committee which will assess the success of the UK's Iranian policy. Mr Ashoori, 66, a retired engineer, was detained in 2017 and was later jailed for 10 years accused of spying for Iran. He is being held at Evin where he recorded a seven-day audio diary for The National recounting the failures of the regime to keep inmates safe from the coronavirus epidemic. “Mr Ashoori has been held hostage by Iran on arbitrary charges since 2017,” said Ms Daby. “It is clear that his detention is part of Iran’s hostage diplomacy drive which is linked to other matters of disputes between the UK and Iran, most notably the historical arms debt. “It is time the prime minister appoints an envoy with the authority and a clear remit to clear the debt and secure the release of hostages to overcome the interdepartmental disputes and bureaucracy. “If the Iranian authorities are serious about resolving this debt, they must also do their part by ending their de-stabilising activities in the region.” Iran has detained dozens of dual-nationals but recognises them only as Iranians, denying them consular access. It has struck prisoner swap deals with governments including France and the United States. President Donald Trump made securing the release of US citizens a plank of his election campaign and appointed a special envoy for hostage affairs. Mr Ashoori’s family said the UK should follow the US lead. “That person should be an impartial person with diplomatic experience,” said Sherry Izadi, Mr Ashoori’s wife.