Nazanin Zaghari-Ratcliffe, the British-Iranian woman jailed in Iran, has not been taken to court to face new charges as expected.
Iranian state media had said she would be required to face fresh charges four years after her initial conviction.
Mrs Zaghari-Ratcliffe was only informed by the prosecutor’s office on Tuesday that the new trial was to take place on Sunday but no official car arrived on the day to take her to court.
Her lawyer was only able to tell her the case had been postponed and that the prosecutor’s office said she would be asked to come to court in the next few days to hear what would happen next.
Speaking to her husband, Richard Ratcliffe, from her parents’ home, Nazanin said: "I would have rather it happened today. I do not sleep at all while the case is hanging over me. This morning I wanted to get it over with – to know where I stand now rather than continue with this whole stupid game."
Detained in April 2016 on charges of spying Zaghari-Ratcliffe had been due to complete her five-year sentence next spring.
The Foreign Office reacted to the news of the postponement by calling on Iran to permanently release Mrs Zaghari-Ratcliffe.
Director of Amnesty International UK Kate Allen said there had already been a "deeply unfair trial" leading to her being "unjustly convicted".
She added: "It appears the Iranian authorities are playing cruel political games with Nazanin. The situation has gone on long enough. Nazanin has continued to suffer in Iran away from her husband and young daughter."
Allen said that the governments has had four and a half years to secure her unconditional release and have failed to do so.
"As a matter of urgency, ministers now need to step up their efforts to get Nazanin home in time for Christmas and provide a clear plan on how they will do this."
Mrs Zaghari-Ratcliffe was released from Evin prison in Tehran in March after coronavirus swept through Iranian jails, but was forced to wear a tag keeping her within 300 metres of her parents’ home.
She told the court on Tuesday that far from facing fresh charges, she believed she had met the criteria for full release as previously pronounced by the supreme leader, Ayatollah Ali Khamenei.
Her husband, Richard Ratcliffe, said she had been "terrified" about the expected court appearance and had suffered the latest in a series of panic attacks.
Explaining the process surrounding Sunday's postponed court appearance, he said: "Nazanin's lawyer went to court early this morning as appointed. When he got there, he was told by the Court Office that there would be no hearing today.
"He had been given no indication that the trial would not be happening until this point. We have not been given a rescheduled date for the court hearing. It is perhaps early to understand why today's sudden postponement happened, or what it means."
A spokesperson for the Foreign Office said: “We welcome the deferral of this groundless court hearing, and call on Iran to make Nazanin’s release permanent so that she can return to her family in the UK.”
Mr Radcliffe believes his wife and other dual nationals are being held hostage because Iran wants the UK to pay a decades-old debt over an arms deal that was never fulfilled.
The UK owes Iran about £400m for Chieftain tanks ordered by the former Shah of Iran which were never delivered because of the 1979 Islamic revolution.
Both the UK and the Iranian governments say there is no link between the outstanding debt and the continued detention of Zaghari-Ratcliffe.
Her case may also be closely linked with the standoff between the west and Iran over the fate of the nuclear deal signed in 2015, and the lifting of the UN embargo on conventional arms sales to Iran that is due to take place in October.