Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori were among a number of people arrested and jailed in Iran.

The report determined that the British government wasted numerous opportunities to secure their release.

The committee said fear of annoying the US and taking legal advice that was later dismissed were among the reasons why the Foreign & Commonwealth Office had proved “ineffectual” at retrieving Zaghari-Ratcliffe or Ashoori sooner.

It added that broader government disorder — marked by secrecy, lack of coordination and successive ministerial appointments — had hindered the FCO’s ability to operate effectively.

The report said in many cases, progress was only made in securing the release of detainees due to public pressure being brought against ministers.

It also found that the initial refusal to engage with Iran over the repayment of $500 million owed from a failed tank deal in the 1970s had actively hindered relations and negotiations over individual releases.

“We heard from a number of families in private that there was a significant trust deficit between them and the government, primarily brought about through poor communication and lack of transparency on the part of the government,” the report said.

“Families are frequently assured by officials and ministers that they are ‘doing all they can’ to secure the release of their detained family members. This is an inadequate response.

“To communicate standard diplomatic representations as substantive actions to families of detainees with little or no further detail is not conducive to a constructive and supportive working partnership.”

Two former foreign secretaries, Boris Johnson and Liz Truss — both of whom later served as prime minister — were named as having “let down” families while in post for making inaccurate statements about specific cases.

Truss was also heavily criticized for her behavior in the failed attempts to secure the release of US-UK-Iranian environmentalist Morad Tahbaz, who was set to be released alongside Zaghari-Ratcliffe and Ashoori but remains imprisoned in Iran.

After the terms of Tahbaz’s release changed, Truss “failed to let either the family or US officials know that Morad was not to be released,” the report said.

“Liz Truss eventually called the family to say that ‘Morad is now a US problem,’ implying that she would not put further effort into his release, and she did not have time to speak to them further.”

Another former foreign secretary, current Chancellor Jeremy Hunt, was criticized for wrongly saying Zaghari-Ratcliffe had received diplomatic protection from the government while in prison.

“This episode serves to illustrate an inconsistent and, at times, clumsy approach by the government,” the report said.

The committee’s chair, Alicia Kearns, described “ministerial clumsiness, serious and avoidable errors and even callous and hurtful comments to families” as having been mentioned repeatedly by victims’ families while describing their experiences.

Names of detainees were often misspelt or mispronounced by officials, Kearns said, and “for dual nationals their ‘Britishness’ too often, they felt, was in question.”

She added that “the most heinous failure of a minister” had been telling the Tahbaz family “you’re no longer our problem.”

An FCO spokesperson told The Guardian: “(UK) Consular officials are available 24/7 for families to receive tailored support. The foreign secretary and (FCO) ministers are fully engaged in complex cases and have raised concerns with foreign governments.”