Houthi rebel leaders reneged on a promise to release a British prisoner held for more than four years without charge in Yemen during a major prisoner swap last year, a senior UK official has told his family. Chief Houthi negotiator Mohammed Abdulsalam assured a British minister at a meeting in Oman's capital Muscat last year that Luke Symons would be released during an exchange of hundreds of prisoners in October 2020. But the British citizen was not included in the group handed over, according to an account given to his family. About 1,080 Iran-backed Houthi rebels and pro-government fighters were flown between the capital Sanaa and Aden under the prisoner exchange deal struck at UN-supervised talks in Switzerland. Another 200 Houthi supporters were allowed to return from Oman. Mr Symons remained in prison while a US humanitarian worker and a businessman were released after intense pressure on the Houthis from the US government. The remains of a third American captive were also repatriated. A British MP and the outgoing ambassador for Yemen said that Mr Symons, who married a Yemeni woman and has a young son, was supposed to be part of a deal but the family missed out. Officials blamed infighting within the upper ranks of the Houthi rebels for the change. Kevin Brennan, the MP for Cardiff West, where Mr Symons's family live, said in a letter to rights group Amnesty International that Mr Symons's role in the exchange was “inexplicably withdrawn”. Mr Brennan said he was told by the UK’s Middle East minister James Cleverly that “lines of communication eventually broke down and talks collapsed”. And in a phone call to the family, the outgoing UK ambassador to Yemen, Michael Aron, said that Mr Symons was not released because of a failure to get him, his wife and their child to the airport in time. “The Americans were working on this deal, as we were, with the exchange on the plane that went in to Oman,” he told Robert Cummings, the grandfather of Mr Symons, according to a transcript of the conversation. “It all came down to not being able to get Luke and his wife and child to the airport in time to get the flights out.” He said that the UK was in discussions with Oman for “weeks and weeks” about sending another aircraft, but this came to nothing. Mr Aron said the negotiator promised both him and the minister that Luke and others would be released once the Houthi wounded were returned from Muscat. He told the family the negotiator “made the commitment and he broke it”. “What can I say? … I wouldn’t say he is the worst of them but he certainly hasn’t been helpful on this,” Mr Aron said, according to a transcript of the phone call. Mr Aron apologised to the family for the failure to secure Mr Symons’s release but denied his case had been ignored by the British government. “We have not succeeded because the Houthis are an unreasonable, unreconstructed bunch of extremists,” he said. “It doesn’t suit their purposes to let him go ... they don’t listen. They are not subject to pressure.” Mr Symons’s family is furious at the failure of the UK to secure his release by using its influence in the region. Mr Brennan cited Mr Symons’s case at a meeting this week in Westminster to discuss the detention in Iran of Nazanin Zaghari-Ratcliffe. He complained of the “UK’s seeming inability to get our people held captive overseas released” compared with other countries. “I’m concerned about whether they are really giving this the full attention that it deserves,” he told <i>The National</i>. “They say to me that it’s a priority and are making every effort but it’s extremely frustrating that no progress has been made on this.” Mr Symons left Cardiff to travel to Saudi Arabia in 2012 to increase his knowledge of Islam, before travelling to Yemen. He met his wife in 2014 but her personal documents were destroyed when their home was bombed in Taez, south-west Yemen, during the conflict. Mr Symons’s efforts to secure travel documents from British authorities for his wife during trips to Djibouti and Ethiopia ended in failure, and he returned to Yemen. He was arrested at a security checkpoint in Sanaa in April 2017. He was only detained because he was carrying a British passport when he was stopped, his family says. Mr Symons has been accused of being an Al Qaeda sympathiser and a British spy — claims denied by his supporters — and has never been charged or put on trial. The British government says that he has been “illegally detained” and has repeatedly called on the Houthis to release him. His wife has been allowed to see her husband sporadically. She told Mr Symons's family that he was showing signs of ill-treatment during her last visit earlier this month. He has told family that he was beaten by guards during his first six months in detention. Mr Cummings said: “He has been suffering for nearly five years and it’s getting worse. His wife had a visit last week and she said that he was in a state and that he broke down. “He has just had enough now.” The UK government says that it has consistently raised the case at the highest levels of the Houthis. UK officials declined to comment on the specific exchanges with Mr Symons's family after the deal broke down. “We appreciate this is a difficult time for Luke Symons and his family,” said a Foreign Office representative. “Our staff have been working intensively, and are engaging at all levels with regional partners, to secure his release.” The war in Yemen began in 2014 when Houthi rebels seized Sanaa. A Saudi-led coalition intervened the following year to support the internationally recognised government.