'You must develop a nuclear bomb for us,' Mr Takriti told Dr Shahristani, who until his resignation two years earlier had been Iraq's top nuclear scientist. 'We need the bomb desperately to rearrange the map of the Middle East.'
Dr Shahristani quit as scientific adviser to Iraq's nuclear energy programme after Saddam came to power in 1979 with plans to convert it to military use. As a result, he was imprisoned in Baghdad's Abu Ghraib (Father of the Estranged) jail.
'I told Barzan (Saddam's favourite smoothtalking troubleshooter) that I did not have the scientific background to make them the bomb,' Dr Shahristani says. 'He replied that anyone not willing to serve their country did not deserve to be alive.
'The minister for higher education, who hadn't said a word so far, started assuring me that Barzan didn't mean it. Barzan interrupted to assure me he did. 'I told him I had a different view of what constituted service to my country. After that, they put in me in solitary confinement for 10 years.'
In Abu Ghraib now, Shia families are having to collect the bodies of young male relatives, summarily executed as part of Saddam's campaign to depopulate the marshes.
The road that took Dr Shahristani from Abu Ghraib to London - where he arrived last week to draw attention to the extermination of Shias - is an extraordinary one.
'Saddam had given personal orders that no one should contact me, except one person, a specially assigned Mukhabarat agent. But because his sort are too proud to carry trays of food to prisoners, they use other prisoners as servants to do it. One young prisoner assigned to me started sympathising with me. He told me he had access to the car of a security guard.
'At first, I didn't act on it, because I thought I wouldn't be able to rescue my family. But during the 1991 Gulf war, it seemed the Mukhabarat's installations were weakened and I would be able to do so.
'So I fled, during the war, by taking the car of the security guard and driving it through four gates. I picked up my family and we drove to Sulaymaniyah in the north. We pretended we were just fleeing the war.'
After that, the family moved to Tehran. From there, Dr Shahristani, a Shia from Kerbala, began his campaign to draw attention to the extermination of the Marsh Arabs. He went to see the then United Nations secretary-general, Javier Perez de Cuellar, in Geneva. 'There I had word that Barzan's men were after me again. I just stayed in my room for a few days. I don't particularly want any protection.'
Last week he visited the Foreign Office where he urged international action over Saddam's campaign in the marshes. He is an able advocate, and carries a large map he has made detailing developments in the area.
The waterways, home to a peaceful people for millennia, have been poisoned and are now being drained by Iraqi engineers. After their failed uprising against Saddam in 1991, the defeated Shia insurgents took refuge in the marshes. Though the allies declared a no-fly zone over the area to prevent attacks by the Iraqi air force, nothing was done on the ground.
The Iraqi army was therefore was able regularly to shell the villages. And engineers poisoned the waterways, poison gas was used on rebel bases, and the 'Third River' was dug to drain the marshes. Most of the 250,000 inhabitants have fled, more than 10,000 to makeshift camps in Iran.
British diplomats say that Dr Shahristani's testimony clarified the picture in southern Iraq. But a safe-haven operation, along the lines of the 1991 'Operation Provide Comfort' in northern Iraq, is not on the cards.
'The difference is that, in the north, the Iraqi troops had withdrawn, so we could park there without trouble,' one diplomat said. 'In the south, we would have to dislodge them. It's also a hellishly difficult area for tanks - that is, until Saddam turns the marshes into a desert altogether.'
Another problem is that such an operation would require a base near Iraq's borders, and Iran is the only option. Conspiracy theorists say that the West is reluctant to help the Shias because it does not want to see the emergence of another Shia state, that could serve as a vector for increasing Iranian influence.
All in all, it looks like Dr Shahristani has a good deal more travelling to do.