Nazanin Zaghari-Ratcliffe has been summoned to an Iranian court next Monday for a new trial.
The British-Iranian, under house arrest in Tehran since being moved from jail in March due to the coronavirus pandemic, has been told to expect to return to prison, according to her husband Richard.
The charity worker is nearing the end of her current five-year sentence after being jailed on spying charges in 2016.
She has always denied the charges.
Richard Ratcliffe, said the Iranian summons came only days after British courts delayed, by six months, an imminent hearing over a legal dispute between Iran and the UK about an outstanding debt which dates back to before the 1979 revolution.
Mr Ratcliffe said he had spoken to Foreign Secretary Dominic Raab and urged him to ensure British diplomats can attend the court proceedings.
"We don't know what will happen on Monday. We don't know how far and how soon they will take forward their prison threat. But we do know that the Revolutionary Guard are signalling something to the British government. And we also know they are signalling this could have a long time still to run," he said.
"We do think that if she's not home for Christmas, there's every chance this could run for years.
"So I really hope there's something we're not being told, as on the face of it, the government's response seems disastrous."
Mrs Zaghari-Ratcliffe was arrested in April 2016 while travelling to visit her parents with her young British-born daughter, Gabriella.
The dual national was sentenced to five years in prison over allegations of plotting to overthrow the Iranian government, which she denies. Prior to her arrest, she lived in London with her husband and child.
Last month, she was told she would face a new trial.
In response to the latest development, the Foreign Office said in a statement: "This latest recall to court is an unwarranted, unjustified and unacceptable decision, which is causing enormous distress to Nazanin Zaghari-Ratcliffe and her family.
"It further tarnishes Iran's reputation. Iran must end the arbitrary detention of all the dual British nationals in its detention, and allow them to return home."
Mr Ratcliffe maintains 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.
"It is imperative that the UK protects Nazanin," he said.
"I told the Foreign Secretary that I felt the UK is dancing to Iran's tune, and exposing Nazanin to abuse because of it."
"Nazanin's case shows clearly that abuse is not something ended by shiny promises and abuser accommodation, but by action and accountability - that applies to all kinds of crime, even hostage taking."
Mr Ratcliffe said his wife had told him over the phone she was feeling "desperate".
"I am dying of this stress - of being taken back [to jail]," she told him. "I can't stop thinking about it. I envy everyone that is free."
Mrs Zaghari-Ratcliffe's family and the UK government have always maintained her innocence and she has been given diplomatic protection by the Foreign Office - meaning the case is treated as a formal, legal dispute between Britain and Iran.
The family's local MP Tulip Siddiq said the timing of the new trial raised "serious concerns".
"Nazanin has once again been treated with utter contempt and I am extremely concerned about her future and wellbeing," the MP for Hampstead and Kilburn said in a statement.
Ms Siddiq said she hoped there was work going on "behind the scenes" to resolve the issues surrounding the historic debt to Iran, adding "Nazanin, as ever, is paying the price".