Nazanin Zaghari-Ratcliffe was forced to sign a "false confession" in front of a UK government witness before she was allowed to leave Iran after six years on fabricated charges of trying to overthrow the regime.
The British-Iranian dual citizen said the signing was captured on camera by the Iranians at Baghdad International Airport and she expects the video to be used against her, she told the BBC.
Ms Zaghari-Ratcliffe was freed along with Anoosheh Ashoori, another British-Iranian, after the UK paid £400 million ($503.4m) debt to Tehran over an arms deal that was aborted after the 1979 revolution.
The charity worker said she was taken to the airport by Iran’s Islamic Revolutionary Guard Corps without seeing her parents in March when she was due to be freed.
"Instead I was made to sign the forced confession at the airport in the presence of the British government," Ms Zaghari-Ratcliffe said.
"They told me that 'you won't be able to get on the plane'. And I knew that that was like a last-minute game because … they told me that they had been given the money.
"So what is the point of making me sign a piece of paper which is incorrect? It's a false confession."
"The whole thing of me signing the forced confession was filmed," Ms Zaghari-Ratcliffe said. "It's a tool. So I'm sure they will show that some day."
Her husband Richard Ratcliffe this month alluded to "mistakes made at the end" of her ordeal in Iran.
Speaking after his wife's first meeting with UK Prime Minister Boris Johnson since her release, Mr Ratcliffe said: "I think there are lessons to learn, there is a wider problem.
"We talked about the mistakes made at the end. It was rough at the end and I think, when Nazanin is ready to talk about it, that is something that we need to go through."
Solitary confinement 'quiet form of torture'
During the BBC TV interview, Ms Zaghari-Ratcliffe revealed the months she spent in solitary confinement at the start of her detention.
"Solitary confinement, in my opinion, is the most hostile, quiet form of torture," she said.
Ms Zaghari-Ratcliffe said she was kept in a one metre by two metre cell with no window, and lights that were kept on all day and night.
"I think solitary confinement works in the way they can mess your mind up in a way to break you," she said.
"There is a reason they keep people in solitary and that is to force them to confess to things they haven't done, and that works."
Ms Zaghari-Ratcliffe, 43, said that before her detention she was not a practising Muslim, but during solitary confinement her faith "got a lot deeper and a lot stronger".
"My faith, more than anything else, helped me," she said. "I felt like this [faith] is very strong inside me and maybe God is testing me in a way."
Daughter's visits source of survival
When she was moved to a general area of the prison, she said her daughter Gabriella's visits were "the source of my survival in prison".
"Gabriella was the youngest of the kids of the mothers in the ward, and the next child was about eight years old,” Ms Zaghari-Ratcliffe said.
"She was two, two and a half when I was moved to the general ward. It was heart-breaking to see a child as young as that to come to see her mother."
Boris Johnson blunder led Iranians to believe she was a spy
She also criticised Mr Johnson for wrongly saying in 2017 that she had been training journalists in Iran.
In 2017, when he was foreign secretary, he erroneously told a foreign affairs committee that Ms Zaghari-Ratcliffe was "teaching people journalism" in Iran.
She had been a project manager for the Thomson Reuters Foundation when she was detained, but she insisted her trip to Iran was a holiday to see her parents.
She said Mr Johnson's mistake helped Iranian authorities to claim she was a spy.
Ms Zaghari-Ratcliffe said she explained this to Mr Johnson at a meeting in Downing Street this month.
"For about a year and a half, I was trying to say: 'Look I was on holiday … I have come with a baby, with a suitcase full of nappies'.
"But then when he made that comment, the Revolutionary Guards every time after that … they said: 'You have been hiding information from us. We know that you're a spy. We know what you were up to, even your prime minister mentioned that.'
"So I lived under the shadow of his comment psychologically and emotionally for the following four-and-a-half years after that day."
Nazanin unable to look at daughter's baby photos
Ms Zaghari-Ratcliffe talked about her daughter, who was two-years-old when her mother was first detained.
Gabriella initially remained in Iran with her grandparents after the arrest. But she returned to the UK to live with her father in 2019.
Gabriella, now 7, did not see her mother again until her release in March this year.
"There was a huge amount of videos and pictures that my family had taken of her when she was away from me,” Ms Zaghari-Ratcliffe said.
"I just couldn't. I still can't go through with them.
"I had a lot of her baby toys and baby clothes in Iran collected to be shipped back with me to London. And they finally arrived. I couldn't open them.
"So there is this legacy, the emotional legacy that will stay with me forever."
Nazanin unsure if she will ever be able to move on
Ms Zaghari-Ratcliffe also revealed that after her return to the UK, her first days were spent with Gabriella and her husband at a safe house.
"Those first nights were like a holiday," she said. "I don't think I will be ever be able to explain the feeling of three of us.
"Also, I knew that my return journey was never going to be rosy, it would be difficult."
"Every day there is one little thing in the house — a picture or a memory of the past — that throws me back to where I was.
"I don't think I have quite managed to close that and move on, and I don't think I will be able to."
Nazanin and Richard's 'love has got a lot deeper'
She concluded her interview by talking about her husband, Richard, who campaigned tirelessly for her release and staged a 21-day hunger strike.
"I've got so much respect for him. I've got so much gratitude,” Ms Zaghari-Ratcliffe said.
"And I think I would never be able to thank him enough.
"It has been an amazing journey for both of us. If anything our love has got a lot deeper."