Liz Truss told the family of a Londoner imprisoned in Iran that he was no longer her "problem" when he was not released as expected with Nazanin Zaghari-Ratcliffe, MPs have claimed.
The then-Foreign Secretary suggested to Morad Tahbaz's family that he would be included in a deal to release detainees in March last year, a report by the Foreign Affairs Select Committee revealed on Tuesday.
Ms Truss agreed to include the UK-US-Iranian trinational in the pact to return Ms Zaghari-Ratcliffe and Anoosheh Ashoori to the UK, in return for the Americans helping broker the arrangement.
"However, Liz Truss did not stand by this arrangement and failed to let either the family or US officials know that Morad was not to be released with Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori," the report said.
Instead of being informed by the Foreign Office or the Foreign Secretary, the Tahbaz family learnt about Ms Zaghari-Ratcliffe and Mr Ashoori's release through news reports.
The report added: "It was, instead, left to senior US State Department officials to formally notify them that Morad had not been released. Liz Truss eventually called the family to say that 'Morad is now a US problem'.
The former Prime Minister hit out at the claims, insisting that "many of the assertions in the report are not true" and the "US did not help broker the deal".
But Tory MP Alicia Kearns said ministers "deeply distressed" British citizens imprisoned abroad through poor communication, including "speaking offensively" to their families.
The chairwoman of the Commons Foreign Affairs Committee added that the treatment of some hostages' families had been "insensitive and hurtful".
Referring to Ms Truss's handling of Mr Tahbaz's case, she said "the most heinous failure of a minister" was to tell a family "you're no longer our problem".
Mr Tahbaz, who was born in London, was working as a conservationist with the Persian Wildlife Heritage Foundation in January 2018 when he was arrested and accused of spying by the Iranian authorities.
The 67-year-old was jailed in 2019 and has been held in Tehran ever since.
His wife Vida, 62, was also banned from leaving Iran. In an interview with the Standard last year, their daughter Roxanne Tahbaz criticised Boris Johnson’s Government, and Ms Truss, for failing to secure the release of her father.
The family told the committee Ms Truss claimed she had secured an "indefinite furlough" for Mr Tahbaz from prison and his wife's travel ban would be removed and she would be free to leave Iran.
Mr Tahbaz was released on the same day charity worker Ms Zaghari-Ratcliffe and retired civil engineer Mr Ashoori were freed but returned to prison soon after their plane took off.
He was released on furlough for three months later in the year which the family argue was "only achieved through the pressure and hard work of Oman and USA".
The committee added that Ms Truss gave "inaccurate descriptions" to Parliament over her communications with Mr Tahbaz, which she subsequently corrected.
He remains in Iran's Evin Prison.
A spokesman for Liz Truss said in a statement to the Standard: “Many of the assertions in the report are not true. The US did not help broker the deal.
"It was always the case that as Morad Tahbaz was also a US citizen, the maximum on the table in any deal with the UK was securing furlough, which was achieved. Morad’s family were aware of this and were kept informed of developments throughout. Without the action Liz took, Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori would still be in jail today.”
