Interspersed through the first 45 minutes of the new film about the killing of Osama bin Laden, Zero Dark Thirty, are scenes of CIA agents torturing a suspect named Ammar. The torture takes place in an anonymous facility and I suppose you could call it generic in nature: the victim is deprived of sleep, beaten, confined in a small space and waterboarded. Eventually he gives up fragments of information that lead US Navy Seals to Bin Laden's compound.

The obvious conclusion is that without this brutality Bin Laden would be alive and still free to attack the US. But there is a problem with the apparently unflinching realism of Kathryn Bigelow's film. Drawing on millions of pages of CIA documents, the US Senate intelligence committee has concluded that intelligence work, rather than torture, led to Bin Laden. So, it seems that scenes conceived with the same bent logic as the Fox network TV series 24, where torture was routinely shown to elicit vital information, were included for dramatic, political or even pornographic effect.

The realism that Bigelow and her writer, Mark Boal, affect is false because of this inaccuracy about the hunt for Bin Laden, but more importantly because even this explicit scene does not touch the reality of what occurred in the "war on terror". The reality is much harder to bear.

Bigelow should try the story of Sami al-Saadi. Or better still, listen to his daughter Khadija, who gave the most chilling account to the BBC of his rendition to Libya as part of a deal struck with MI6's Mark Allen, for which the Saadi family is now in receipt of £2.2m from the British government.

Imagine the fear of the Saadi kids as they were separated from their parents and flown from Hong Kong to Bangkok, where the plane picked up five of Muammar Gaddafi's men. They didn't know their parents were on the plane until it landed at Tripoli and Khadija saw her father handcuffed and with a needle in his arm. Then they met Moussa Koussa, Gaddafi's intelligence chief, and the years of Saadi's imprisonment and torture began.

Nothing in Bigelow and Boal's film could capture the terrible effects of rendition and torture on the victims and their families, nor, for that matter, the hypocrisy of western governments that outsourced brutality and whose representatives watched as people were sodomised and electrocuted and cut, while leaders reassured themselves that this was the grown-up world of realpolitik.

Tony Blair clinched the desert deal with Gaddafi that rendered two of the dictator's enemies – Saadi and Abdel Hakim Belhaj – but now he circles the world with his Faith Foundation. Sir Mark Allen, who apparently dined with Koussa at the Travellers Club and whose correspondence with Gaddafi's former intelligence chief allowed the two Libyans to bring a case against the British government, muses about the sacred mysteries of religion for the Catholic Herald.

This is from Allen's recent article about the visit of a reliquary of St John Vianney, the Curé d'Ars, to Britain. "The visit of the heart of St John Vianney will reach out to many and touch them in comforting and wonderful ways. Thus, the mysterious power of the holy, its impact and influence, comes into our lives. And we are attracted by it. Our deepest nature responds."

Hold that in your mind and read the note to Koussa after Belhaj and his pregnant wife were rendered to Tripoli. "I congratulate you on the safe arrival of [Belhadj]. This was the least we could do for you and for Libya. I know I did not pay for the air cargo [but] the intelligence [on him] was British." In another note, Allen was specific about the kidnap of the Saadi children in Hong Kong.

Neither I, in the espionage thrillers I have written, nor perhaps even the great John Le Carré could have dreamed up a spy that harbours this particularly ripe hypocrisy. It seems too unbelievable, yet the sanctimonious self-worth evident in Blair, Allen and the former foreign secretary Jack Straw, who, incidentally, seems to have misled the House of Commons on Labour's involvement with rendition, is precisely what allowed Britain to ignore torture treaties and render men to have their fingernails pulled out.

"I feel so angry and sad," said Khadija. "A country like England is supposed [to] be [a] democracy and support the human rights."

Perhaps Blair and the rest of them did not trouble themselves with visions of what might befall her family, or Belhaj and his wife, yet they let it happen nonetheless, despite their public piety. And that's the point – all governments panic and lose their way, and some ministers and civil servants, whatever they tell us about themselves, are capable of behaving very badly indeed. That's why any proper free society has systems of control and scrutiny, and insists on accountability, even of its intelligence services.

It is essential to understand that none of what happened to the Saadis or Belhaj would have come to light had it not been for the chance discovery by Human Rights Watch of documents in Koussa's office, which established Allen's eager co-operation on behalf of the UK. The evidence was so strong that the government simply settled with Saadi, even though, of course, it did not have the guts to admit liability.

But what would have happened if the justice and security bill, currently going through parliament, had already been passed and the system of secret court hearings was in force. The government would have ordered a "closed material procedure" and fought Saadi in camera, and all the evidence would have been secret, and remained so forever.

If this bill passes, the public will be deprived of knowledge of any case that is remotely embarrassing to ministers and spies, and as a result people like Blair, Allen and Straw will be able to act with an absolute lack of public scrutiny – that is, with impunity. This is a very serious attack on our system of open justice, and what is absolutely without conscience is that the prime minister is now using the Saadi case to argue that secret courts will increase rather than diminish the justice available in Britain.

As the campaign group Reprieve suggests, politicians are simply not to be trusted with a dangerous new power that closes off courts for their own convenience. In camera or on camera, the subject of torture is too serious for politicians to be allowed to hide in secret courts and for filmmakers to reduce the experience of endless pain and despair so that it seems just about justifiable.