A new trial faced by British-Iranian woman Nazanin Zaghari-Ratcliffe has been postponed at short notice with no future date set.
The 42-year-old woman has been detained in Iran since 2016, when she was sentenced to five years in prison over allegations, which she denies, of plotting to overthrow the Iranian government.
Her husband Richard Ratcliffe has said the new charges against his wife were further evidence she is being held for "political leverage" amid a multimillion pound dispute between Britain and Iran.
This week Prime Minister Boris Johnson described the decision to bring new charges as "indefensible and unacceptable", according to Downing Street.
A Foreign, Commonwealth and Development Office spokeswoman 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."
Amnesty International UK accused the Iranian authorities of "playing cruel political games" with Zaghari-Ratcliffe, and called on the UK Government to make it their "absolute priority" to get her home for Christmas.
Kate Allen, director of Amnesty International UK, said: "Nazanin has already been unjustly convicted once after a deeply unfair trial.
"It is a nonsense that she should ever have even faced a second court date.
"The situation has gone on long enough.
"Nazanin has continued to suffer in Iran away from her husband and young daughter.
"The UK government has had four and a half years to secure her unconditional release and has failed to do so.
"Securing Nazanin's release should be an absolute priority".
It has been claimed Mrs Zaghari-Ratcliffe is being held in order to force the UK into settling a multimillion pound dispute with Iran.
The debt dates back to the 1970s when the then-shah of Iran paid the UK PS400 million for 1,500 Chieftain tanks.
After he was toppled in 1979, Britain refused to deliver the tanks to the new Islamic Republic and kept the money, despite British courts accepting it should be repaid.
Australian Associated Press