Iran's supreme court has upheld a five-year prison sentence given to a British-Iranian woman for security offences.
Charity worker, Nazanin Zaghari-Ratcliffe, was arrested at Tehran Airport in April 2016 while visiting family in Iran with her daughter.
The 38-year-old, who maintains her innocence, has lost the final stage of her appeal against the sentence.
Her husband said there were no more legal options to overturn the sentence.
She was accused of allegedly plotting to topple the government in Tehran, but the official charges against her have not been made public.
Iran refuses to recognise dual nationals and denies them access to consular assistance.
The Foreign and Commonwealth Office has said it is "deeply concerned" by the latest court decision.
The British ambassador to Iran visited Mrs Zaghari-Ratcliffe's two-year-old daughter Gabriella last year, who has been placed in the care of her Iranian grandparents, after the Iranian government confiscated her passport.
A spokesman for the FCO said: "Iran continues to refuse the UK access to her. The prime minister and foreign secretary have both raised Mrs Zaghari-Ratcliffe's case with their counterparts in Iran.
"We continue to press the Iranians for access and for due process to be followed, and are ready to help get her daughter back safely to the UK if requested."
But speaking from the UK, Mrs Zaghari-Ratcliffe's husband, Richard, said he would continue to put pressure on the UK government.
"We've had a year, the legal process is finished, so I think the government needs to step up, find a way to visit her, say that she's innocent and call for her release publicly," he said.
"As her husband, I can say Nazanin is innocent until I am blue in the face. I have spent a year doing it.
"But it makes a clear difference that the government hasn't. It indulges the whispers."
Monique Villa, CEO at Thomson Reuters Foundation, said she was "entirely convinced" of Mrs Zaghari-Ratcliffe's innocence and called for her immediate release.
She said: "This extinguishes the last hope we have had of legally overturning a punishment where the crime remains a mystery.
"Nazanin was given no court hearing for this final judgement. She is not a spy but an innocent mother who travelled to Iran only to show her baby to her parents."
Ms Villa added that Ms Zaghari-Ratcliffe has never had dealings with Iran in her professional capacity at the Thomson Reuters Foundation.