Nazanin Zaghari-Ratcliffe said she was forced to sign a “false confession” in the presence of the UK government before being allowed to leave Iran.
The Anglo-Iranian hostages survive described the action captured on camera as “dehumanizing”.
She said she hopes Tehran will use it against her in the future.
While ‘forced’, the 44-year-old charity worker claims she was forced to admit charges of Iranian espionage after they detained her for six years – an allegation she and the UK negate.
She said she was taken to the airport by the Revolutionary Guards without seeing her parents on the day of March when she was released.
Ms Zaghari-Ratcliffe told the BBC: “Instead, I had to sign a rape confession at the airport in the presence of the British government.
She was then told by the Iranians that the UK had settled a historic £400m debt from the 1970s.
“They told me ‘you won’t be able to get on the plane.’ And I knew it was like a last-minute game because I knew they were… they told me they were given money,” she said. he said.
“Then what’s the point of making me sign an incorrect piece of paper? It’s a false confession.”
Ms Zaghari-Ratcliffe also told the BBC’s Emma Barnett that a British official was present at the time she signed the document.
“The whole thing that I signed to the rape confession was filmed,” she said.
“It’s a tool. So I’m sure they’ll show it off someday.”
The revelation comes after her husband Richard Ratcliffe alluded to “mistakes made at the end” of the ordeal in Iran.
Speaking earlier this month after First meeting of the lady with Prime Minister Boris Johnson Since her release, Mr Ratcliffe said: “I think there are lessons to be learned, there is a broader problem.
“We talked about the mistakes we made at the end. It was tough in the end, and I think, when Nazanin is ready to talk about it, that’s what we need to go through.”
Meanwhile, at a press conference after her debut in March, Ms. Zaghari-Ratcliffe said the government took too long to pay off a multi-million pound debt to Iran, which secured her release.
She said that while she couldn’t be happier to be home, “this should have happened six years ago”.
Following the comments, she received backlash online from people who said she should be grateful, but Downing Street was quick to defend her.
Boris Johnson’s official spokesman said: “Clearly someone who has been through something like Ms Zaghari-Ratcliffe should not be abused.
“As a UK citizen, she can voice her opinion on any subject she wants.”