Nazanin Zaghari-Ratcliffe said it was made clear to her early on she was being held hostage in order to make money off the British Government.
The British-Iranian political prisoner spent six years held in Iran after being arrested on falsified charges when touching down at the airport to visit her parents in 2016.
The 44-year-old was accused of crimes against national security.
She was said to be running a journalism course that encouraged people to spread propaganda.
In reality, she was simply introducing her 22-month-old daughter Gabriella to her parents.
Her ordeal saw her eventually able to return to the UK in March.
Speaking on BBC One's Nazanin Zaghari-Ratcliffe talks to Emma Barnett on Monday night, Nazanin said it was quickly made clear to her she was imprisoned as a pawn to "get something off the British Government".
She explained: "We are talking about a regime, one of the highest members of the authorities once said we are proud to be taking a couple of hostages every year to make money out of them.
"So, that is the idea, that is the ideology. It’s a strategy.
"They arrest us to make something out of us. They are taking me to get something off the British Government.
"They were very clear about that.
"I think it was week two that I was arrested they said that we want something off the British Government, we will not let you go until we get that.
"And they gradually developed the story and it was a lot clearer," she added.
The Iranians told her the UK had not settled a historic £400 million debt dating to the 1970s.
This was denied for years by the UK but was finally paid when Nazanin was released.
She also told Ms Barnett she was forced to sign a "false confession" in front of a UK Government witness before she was allowed to leave Iran.
She said the act captured on camera by the Iranians was "dehumanising", and that she expects Tehran to use it against her in the future.
While "under duress", she said was forced to admit to the Iranians' allegations.
The charity worker said she was taken to the airport by the Revolutionary Guards without seeing her parents on the day in March when she was to be freed.
In her first press conference since freedom, the British-Iranian mum said her ordeal "will always haunt me" - and she had found it difficult to trust UK Foreign Secretaries to get her home as years ticked by.
In a moving plea, she added the "meaning of freedom is never going to be complete" until Morad Tahbaz and other dual nationals are released and reunited with their families.
"I was the lucky one", she said.
