Nazanin Zaghari-Ratcliffe, 39, was taken to a court on Saturday morning and informed by a judge she was likely to be found guilty of spreading propaganda against the Iranian regime, the Free Nazanin campaign said.
Judge Salavati rejected her choice of lawyer, who had “not been approved”, the campaign added.
Mrs Zaghari-Ratcliffe, from Hampstead, north London, denied the charge as she pleaded for clemency and asked to “go home and have another baby”.
Last week, Mrs Zaghari-Ratcliffe’s husband, Richard, said he feared his wife would be taken back to court on a resurrected charge of spreading propaganda against the regime.
She is already serving a five-year jail term after being convicted of plotting to overthrow the Iranian regime – something she has always denied.
The new charge comes despite a telephone discussion between Theresa May and Iranian President Hassan Rouhani, during which the Prime Minister called for the release of British prisoners held in Iran on humanitarian grounds.
During the hearing on Saturday, Mrs Zaghari-Ratcliffe is quoted as saying: “I have never been involved in overthrowing the regime.
“I do think the government here needs to reform, but I have never been involved in any attempts to change the regime.”
She also spoke about her desire to have a second baby, telling the judge: “This year I am turning 40. I might only have a slim chance.”
Mrs Zaghari-Ratcliffe is said to have added: “There is something called clemency. Give me that for the sake of my baby. She hasn’t seen her father for over two years now.
“I would ask the judge today to close this new case and give me parole, so that I can go home and have another baby and have a normal life.”
The judge said he would address her case “as a priority”.
The Free Nazanin campaign said that the following day Mr Zaghari-Ratcliffe was allowed to phone Rob Macaire, the new British ambassador to Iran, from prison.
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It was the first time she had been allowed any contact with the British embassy in more than two years, the campaign said.
It added that the 39-year-old asked Mr Macaire to try and visit her and requested him “to issue a formal diplomatic note protesting against the new charges” and the “invented case against her”.