In a video interview with independent investigators, Mrs Zaghari-Ratcliffe, 43, revealed she was threatened with execution and the torture of her family.
She was also chained and forced to wear a blindfold in prison where she suffered sensory and sleep deprivation.
The British-Iranian aid worker, from North London, was interrogated for up to nine hours at a time in solitary confinement.
She was bombarded with bright lights and blaring TVs to prevent her sleeping.
Nazanin Zaghari-Ratcliffe (pictured) has told of her five years of ‘traumatising’ torture in Iran for the first time after she was released on house arrest last year
In the investigators’ report, seen by the BBC, she is quoted as saying officials threatened to take away her daughter Gabriella, now six, who was with relatives at the time.
She said they told her that her British husband Richard ‘was a spy, that he had already left me, that he was lying to me, that he worked for the British intelligence service.
‘They said he was unfaithful. They said he was not an accountant and that he had always been lying to me. They told me I had been fired from my job.’ Mrs Zaghari-Ratcliffe was jailed for alleged spying while visiting relatives in Iran in 2016.
She was released on house arrest last year and forced to wear an ankle tag during the pandemic. That sentence ended last weekend and the tag was removed but she faces a new court hearing over separate propaganda charges on Sunday.
She told investigators she was confined to a 6ft by 5ft cell during solitary confinement. She said: ‘The light was left on all the time. There was only a dirty mat on the floor with a thin blanket to sleep on. There were times I could not breathe.’
In 2018 she spent a week in a psychiatric hospital with her hands and feet chained to the bed. In jail her hair began to fall out and she was too weak to climb up to the top bunk in a ward where she was being held.
Richard Ratcliffe, the husband of Nazanin Zaghari-Ratcliffe, with his daughter Gabriella pose for photographers during a protest outside the Iranian Embassy in London, Britain, March 8
The report was commissioned by human rights charity Redress. She has now been diagnosed with post-traumatic stress disorder, depression and obsessive compulsive disorder.
It linked these conditions to due to ‘extremely stressful, traumatising experiences in the prisons of Iran’ and the uncertainty about her fate. The evaluation was carried out by the International Rehabilitation Council for Torture Victims.
Investigators have said there is no chance of a full recovery unless she is brought back to the UK for mental health treatment.
On Wednesday Boris Johnson demanded the ‘immediate release’ of Mrs Zaghari-Ratcliffe in a phone call with Iran’s president Hassan Rouhani.
In a statement, the Foreign Office said: ‘Iran continues to put Nazanin Zaghari-Ratcliffe through a cruel and intolerable ordeal. Nazanin must be allowed to return permanently to her family in the UK.’
On Wednesday Boris Johnson demanded the ‘immediate release’ of Mrs Zaghari-Ratcliffe in a phone call with Iran’s president Hassan Rouhani (pictured in Tehran on Wednesday)
Downing Street said in a statement: ‘The Prime Minister spoke to Iranian President Rouhani this afternoon.
‘The Prime Minister raised the case of Nazanin Zaghari-Ratcliffe and other British-Iranian Dual Nationals detained in Iran and demanded their immediate release.
‘He said that while the removal of Nazanin Zaghari-Ratcliffe’s ankle monitor was welcome, her continued confinement remains completely unacceptable and she must be allowed to return to her family in the UK.’
Mr Johnson and Mr Rouhani also discussed the status of the Iran nuclear deal.
Number 10 said: ‘The Prime Minister also stressed that while the UK remains committed to making the Iran nuclear deal a success, Iran must stop all its nuclear activity that breaches the terms of the JCPoA and come back into compliance.
‘He stressed the importance of Iran seizing the opportunity presented by the United States’ willingness to return to the deal if Iran comes back into compliance.
‘The Prime Minister underlined the need for Iran to cease wider destabilising activity and be a positive force in the Gulf region.’
Ms Zaghari-Ratcliffe’s husband, Richard Ratcliffe, held a vigil, along with the couple’s six-year-old daughter Gabriella, outside the Iranian embassy in central London on Monday.
Mr Ratcliffe attempted to deliver an Amnesty International petition of more than 160,000 signatures calling for his wife’s immediate release, but was turned away by someone speaking over the building’s intercom.
A small group of protesters stood in front of the embassy holding placards carrying the messages ‘Free Nazanin’ and ‘still not forgotten’.
Speaking to the press, Mr Ratcliffe said the recent developments in his wife’s situation were ‘slightly better news than was expected’ but highlighted that she was still being ‘threatened’ with another court case in Iran next week.
Explaining the purpose of Monday’s protest, he said: ‘I wanted to do something just to say listen, she’s not forgotten. We’re still going to keep battling until she’s home.’
He added: ‘It is still the Iranian authorities that are holding Nazanin. They are now holding her even after the end of her sentence. That remains outrageous.’
Ms Zaghari-Ratcliffe, a charity worker who was employed by the Thomson Reuters Foundation, has strongly denied the widely refuted allegations that she was plotting to overthrow the Islamic Republic’s government.
She was arrested at Tehran’s Imam Khomeini Airport while taking their daughter Gabriella to see her parents in April 2016.