The British government has said it would continue to push for the release of a conservationist who was not allowed to leave Iran under the deal that brought two dual citizens home.
Morad Tahbaz, who holds US, UK and Iranian citizenship, was allowed to leave prison four years into a 10-year sentence under the agreement that led to Britain settling a £400 million (£523m) arms debt from the 1970s.
Mr Tahbaz, the only one of the three born in the UK, must remain in Iran as part of the deal. His family is said to be “devastated” that he was not allowed to leave.
Nazanin Zaghari-Ratcliffe, 43, and Anoosheh Ashoori, 67, returned to the UK early on Thursday to be reunited with their families.
A fourth prisoner, Mehran Raoof, a veteran trades unionist who once lived in north London and was sentenced to jail for 10 years during a sweep of human rights activists, has not featured in official UK government statements about the deal.
“The British negotiating position must have been weak indeed if they saw fit to leave half the hostages behind,” said Kylie Moore-Gilbert, a UK-Australian dual citizen who spent two years in prison before the Australian government organised a prisoner swap.
Mr Tahbaz was diagnosed with cancer in 2019 and has been treated within a prison system that is notorious for its poor care.
He was part of a group of conservationists from the Tehran-based Persian Wildlife Heritage Foundation, which had been licensed to operate in Iran by the government in 2018.
A senior figure from the group died while interrogations were held at Evin prison in Tehran, the US-based Centre for Human Rights in Iran. They were convicted after a case based partly on a retracted forced confession.
Ms Moore-Gilbert said a public campaign by Mr Tahbaz would have gone against the wishes of the other seven Iranians arrested with him in 2018.
“Morad is a man in his 60s in remission from cancer who dedicated his life to philanthropy and, in particular, to saving Iran's endangered wildlife,” she said. “I have no doubt that public pressure would have led to his being on that plane alongside dear Nazanin and Anoosheh.”
The Iranians claimed his US nationality made his case more complicated, UK government minister James Cleverly said.
“But we don't stop, we have never stopped and we will continue working to get his full permanent release and his return home to his family," he said.