Nazanin Zaghari-Ratcliffe who was due to end her five-year sentence next spring has been summoned to court next Monday.
The 42-year-old British-Iranian has been under confinement since she was moved from prison in March. However, fresh court proceedings against her cast the timetable into doubt.
On Thursday, Hamid Baeidinejad, Iranian ambassador to the UK was summoned to meet Foreign Office director-general for the Middle East, North Africa, Afghanistan and Pakistan.
Thomas Drew conveyed the UK’s “grave concern” at the move and told the Iranian ambassador to end at Ms Zaghari-Ratcliffe`s “arbitrary detention”.
A spokesperson said: “We have made it clear to the Iranian ambassador that his country’s treatment of Nazanin Zaghari-Ratcliffe is unjustified and unacceptable, and is causing an enormous amount of distress.
“Iran is further tarnishing its reputation through its actions towards Nazanin. It is time to end her arbitrary detention and that of the other dual British nationals it is holding.”
The foreign secretary, Dominic Raab, also condemned her treatment as “unacceptable”.
Mrs Zaghari-Ratcliffe was detained in April 2016 on her way to visit her parents and her parents with her young British-born daughter, Gabriella.
She was accused of plotting to overthrow the Iranian government and sentenced to five-year imprisonment. In March the charity worker was allowed to leave prison due to the coronavirus pandemic but remains under house arrest.
Mrs Zaghari-Ratcliffe denied all the charges and her husband said that he believed Iran was holding his wife and other dual nationals hostage just to make the UK pay the very old debt over an arms deal that was never fulfilled.