Morad Tahbaz, the British-Iranian man who was not allowed to leave Iran as part of the deal struck by the British and Iranian governments freeing Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori, has gone on hunger strike in protest, his family have said. Tahbaz has also been taken from the public ward in Evin prison in Tehran, but it is not known where to, or for what reason, the family said. The family accused the Foreign Office of abandoning him in order to secure the release of Zaghari-Ratcliffe and Ashoori, and revealed that Morad’s 93-year-old mother was taken to hospital on Saturday. His sister Tarane Tahbaz said: “He was released for 10 hours, then 24 hours, before it ended after 48 hours. I am afraid the Foreign Office wanted him out of the way for 48 hours so they could secure their wonderful photo op.” The Foreign Office declined to offer any comment, but on Friday said it had been assured that Tahbaz was being taken back to prison from his family home solely to fit him with an ankle tag before he was put back on furlough. The Foreign Office insisted that as part of the deal freeing the other two dual hostages, British diplomacy had secured his release on indefinite furlough. Any other outcome would be a breach of undertakings given to the Foreign Office. Tahbaz’s failure to reappear at his family home this weekend after being taken back to prison on Friday, and the news that he has gone on hunger strike in protest at the handling of his case, suggests he feels events are moving in the wrong direction. He has British, Iranian and American citizenship, and it appears Iran did not see him as part of the deal. It is also possible that behind-the-scenes diplomacy is working to restore his release. Morad’s sister said there had been no contact from the Foreign Office since Friday. “His condition is dire and he is in prison. This whole furlough business was a farce. We are left deflated, and worrying that this is all now going to be swept under the carpet.” She had briefly seen video images of her brother on an iPhone, and said: “He was barely recognisable, since he has lost 40kg. I only knew it was him when he waved and smiled.” Tahbaz, a conservationist, was arrested in January 2018 along with eight other members of the Persian Wildlife Heritage Foundation. Tarane said: “We were advised by the Foreign Office that the less noise we made, the better it would be for him and his release, so for four years we were told he would be part of the deal if and when it were to be made. It was only after Anoosheh and Nazanin were to be released – about which we are ecstatic – that we found out he was to be left behind. We are very grateful that Nazanin is still lobbying for us now that she is out.” She also disclosed that her 93-year-old mother, Hamideh, had to be taken to hospital on Saturday night because “she had a complete meltdown. Morad’s incarceration has been a terrible blow to her. She really wants to stay alive just to see him. “It was such a shock when he was first arrested. We thought it was a mistake, but when they were given terrible prison sentences, we did not know what to do.” Separately, Ashoori’s wife, Sherry Izadi, thanked Guardian readers for raising money to pay for a sudden £27,000 fine imposed on them by the Iranian government as part of his release. The family had to go heavily into debt to raise the money. Within 12 hours of launching a crowdfunding website publicised by the Guardian, the money was raised. Izadi said: “We are absolutely overwhelmed by the public’s generosity and the hundreds of messages of support and sympathy we have received, These acts of kindness have restored our faith in humanity. We are also hugely grateful to the Guardian, who helped us raise this cash in such a short period of time. “We mark the first day of spring and the start of the Iranian new year with renewed hope and a firm resolve to help reunite the remaining detainees with their loved ones.” The Foreign Office was contacted for comment.