Boris Johnson walked past the hunger-striking husband of Nazanin Zaghari-Ratcliffe and ignored him, it has been claimed.
In a parliamentary debate on Tuesday about the British-Iranian dual national's case, her local MP Tulip Siddiq read out a statement from her husband.
Richard Radcliffe ended his hunger strike after 21 days camped outside the Foreign Office without food in protest at British government inaction on the case.
In the statement he said: "Today marks day 2,054 of Nazanin's detention. We are approaching our sixth Christmas apart. A little girl has been without her mother for five and a half years now. It did not have to be like this.
"The Prime Minister did not visit me on hunger strike, though he did pass me one day without coming over. His Government continues to put British citizens in harm's way, Nazanin's story shames this country."
Ms Siddiq, who has taken up the case, said she was "increasingly frustrated" with the government's approach. She said ministers acknowledged that they owed Iran £400 million and that there was "no question about the fact that the debt is linked to Nazanin's case".
She told MPs: "Richard Radcliffe went on hunger strike because he felt he had no other option, and he went on hunger strike for three weeks outside the Foreign Office in order to capture the attention of the upper echelons of government.
"He did it because he thinks the upper echelons of government are not helping with his wife's plight. I'm very disappointed to say that in the three weeks that Richard was outside the Foreign Office starving himself the prime minister of our country did not come to visit him."
The Labour MP for Hampstead and Kilburn also blasted the prime minister for having "made an enormous blunder while he was giving evidence to parliament".
While foreign secretary Mr Johnson claimed Ms Zaghari-Ratcliffe was teaching journalism while in the country - she says she was in fact visiting family.
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