Nazanin Zaghari-Ratcliffe was tried Monday in Iran and asked to prepare to return to prison, her family said.
The 42-year-old mother of one child, who has been detained in Iran since 2016, is said to pack her bags after a hearing.
She was placed under house arrest in March when thousands of prisoners were granted pardon and released from Iranian prisons during the Covid-19 outbreak.
In September 2016, Ms. Zaghari-Ratcliffe was sentenced to five years in prison after she was convicted of “conspiracy to overthrow the Iranian government”.
Her husband Richard Ratcliffe said she was visited by members of the Iranian Revolutionary Guard (IRGC) at her parents’ home.
In a statement, he said: “We don’t know what’s going to happen on Monday, we don’t know how far and how quickly they will advance their prison threat.
“But we know the Revolutionary Guard is signaling something to the British government.
“We also know that they are signaling that this could take a long time.
“As Nazanin’s husband, I think that if she’s not home for Christmas, there is every chance this could go on for years.
“I really hope we won’t be told, as the government’s reaction seems disastrous at first sight, only extraordinary that they won’t change course.”
The latest development in Mrs Zaghari-Ratcliffe’s case coincides with another six month delay on whether the UK owes Iran £ 400 million.
The Middle Eastern nation claims this based on an arms deal from the 1970s.
Just months after her expected release date, Ms. Zaghari-Ratcliffe was tried in September and said she would face a second trial. However, this has been postponed at short notice with no future date set.
Her husband said he would bring charges of disseminating anti-government propaganda in a case that was dropped in December 2017 after a visit by then Secretary of State Boris Johnson, but reopened in May 2018.
Ms. Zaghari-Ratcliffe’s local MP Tulip Siddiq said the timing of the trial raised “serious concerns” as it stems from the postponement of a trial on Britain’s historic debt to Iran.
The MP from Hampstead and Kilburn said in a statement: “Nazanin has again been treated with the utmost contempt and I am extremely concerned about her future and her well-being.
“The fact that she was told to pack a bag for prison before her trial does not make me confident that it will come close to a fair trial.
“The timing of this development, as well as the postponement of the trial on Britain’s historic indebtedness to Iran, raise serious concerns.
“I can only hope that behind the scenes work is being done to resolve the debt quickly because we seem to be going completely in the wrong direction and Nazanin is paying the price as always.
“The Secretary of State must assert the UK’s right to consular access and ensure that British officials are present at Nazanin’s trial.”