We shouldn't be surprised to hear that George Bush dined with a group of historians on Sunday night. The president has spent much of his second term pleading with history. But however hard he lobbies the gatekeepers of memory, he will surely be judged the worst president the United States has ever had.

Even if historians were somehow to forget the illegal war, the mangling of international law, the trashing of the environment and social welfare, the banking crisis, and the transfer of wealth from poor to rich, one image is stamped indelibly on this presidency: the trussed automatons in orange jumpsuits. It portrays a superpower prepared to dehumanise its prisoners, to wrap, blind and deafen them, to reduce them to mannequins, in a place as stark and industrial as a chicken-packing plant. Worse, the government was proud of what it had done. It was parading its impunity. It wanted us to know that nothing would stand in its way: its power was both sovereign and unaccountable.

Three days before Bush arrived in Britain, the US supreme court ruled that the inmates at Guantánamo Bay were entitled to contest their detention in the civilian courts. This is the third time the supreme court has ruled against the prison camp, but on this occasion Bush cannot change the law: the court has ruled that the prisoners' rights are constitutional.

Symbolically the decision could scarcely be more important. Practically it could scarcely be less. The department of defence can transfer its prisoners to an oubliette in another country, where the constitution's writ does not run. The public atrocity of Guantánamo Bay has provided a useful distraction from something even worse: the sprawling system of secret detention camps the US runs around the world.

We don't, of course, know much about this programme. Bush first acknowledged it in September 2006. "Of the thousands of terrorists captured across the world, only about 770 have ever been sent to Guantánamo." Other suspects, he said, were being "held secretly" by the CIA. "Many specifics of this program, including where these detainees have been held and the details of their confinement, cannot be divulged." He went on to claim that all the secret prisoners had now been transferred to Guantánamo Bay.

Several lines of evidence suggest that this claim was false. The CIA appears to have overseen or controlled, and in some cases appears still to be running, black sites in Poland, Bulgaria, Romania, Ukraine, Macedonia, Kosovo, Morocco, Libya, Egypt, Djibouti, Somalia, Ethiopia, Iraq, Jordan, Afghanistan, Pakistan, Thailand and, possibly, Diego Garcia. The US appears to be using ships as secret prisons. In just two years the CIA ran 283 flights - which the Council of Europe believes were used for transporting secret prisoners - out of Germany alone. It admits that it possesses 7,000 documents about its ghost detention programme. Are we to believe all this was done for the 14 men transferred to Guantánamo Bay? In Iraq, the US now admits to holding 22,000 prisoners without charge in its own facilities, some of whom are known to be kept away from the Red Cross and other visitors.

Apart from those moved to Cuba, hardly anyone, so far, has come out of this system. At the end of last year salon.com interviewed Muhammad Bashmilah, who was arrested and tortured by Jordanian police, handed to the Americans, flown to an unknown country in autumn 2003, and held secretly by the CIA until he was transferred to Yemeni custody in May 2005. He reports that he was kept in a cell about the size of a transit van throughout the 19 months of his confinement, without any human contact except during interrogation. The lights and a source of white noise were left on permanently. Driven mad by isolation and sensory deprivation, he tried to kill himself several times. Eventually, when it became obvious even to the CIA that he had nothing to do with terrorism, he was handed over to the Yemeni government, who held him for another year until he was released without charge.

Lawyers for some of the men transferred to Guantánamo Bay claim that, while in secret detention, their clients were left hanging from the ceiling by their wrists, beaten with electric cables, yanked around on a dog's leash, chained naked in a freezing cell, and doused with cold water. "The CIA worked people day and night for months," one prisoner reports. "Plenty lost their minds. I could hear people knocking their heads against the walls and doors, screaming their heads off."

Could it be worse than this? Yes. In 2003, a US official admitted to the Sunday Telegraph that the CIA was detaining and interrogating children. Discussing two boys aged seven and nine held in secret detention by the CIA, the official explained: "We are handling them with kid gloves. After all, they are only little children, but we need to know as much about their father's recent activities as possible. We have child psychologists on hand at all times and they are given the best of care." According to another prisoner, the boys had already been tortured by Pakistani guards. A former CIA official told the New Yorker that "every single plan [in the secret detention programme] is drawn up by interrogators, and then submitted for approval to the highest possible level - meaning the director of the CIA. Any change in the plan - even if an extra day of a certain treatment was added - was signed off by the CIA director."

Never mind detention without trial; this is detention without acknowledgement. When men and women disappear into this system, neither they nor their families know where they are. The Red Cross cannot reach them; they are beyond the scope of the law. They have been disappeared in the Latin American sense of that word.

Do I need to explain that this treatment breaks just about every article in the Geneva conventions? Do I need to tell you that - without charges, trials, lawyers, scrutiny or even recognition - it is just as likely to net the innocent as the guilty? In 2006 George Bush maintained that "these aren't common criminals, or bystanders accidentally swept up on the battlefield - we have in place a rigorous process to ensure those held at Guantánamo Bay belong at Guantánamo". But a new and detailed investigation by the McClatchy newspaper group has found that many of them were indeed either common criminals or bystanders, or men sold to the authorities in order to settle a feud. Who knows how many innocent people are going out of their minds in the CIA's secret prisons today?

Along with its innocent victims, the US government has locked itself into this system. As the justice department has argued, these prisoners cannot be released in case they describe the "alternative interrogation methods" (the euphemism it uses for torture) the CIA used on them, which could "reasonably be expected to cause extremely grave damage". Like almost everything Bush has done, this programme promises to backfire. George Bush will be remembered not only for the lives he has broken, but also for smashing everything he claimed to defend.

monbiot.com

· This article was amended on Wednesday June 18 2008. We originally referred to "the transfer of wealth from rich to poor", when we meant the opposite. This has been corrected.