When we try to decide on the most destructive aspects of the legacies of George W Bush and Tony Blair, the Iraq war obviously features prominently. But there are other contenders. Will we most regret the reintroduction of abusive interrogation, previously thought to have been laid to rest by the UN Convention Against Torture? Or will the stampede towards greater governmental secrecy in the end do more damage?

I suspect the winner will be governmental secrecy. Blair retrospectively described his support for the Freedom of Information Act as his greatest mistake in government. That was both extraordinary, and extraordinarily sad: to be sure, complying with the act can be an imposition for public servants, yet even FOIA requests did not reveal the extent of the parliamentary expenses scandal. Most references about duck islands and even criminal offences were redacted out of the FOIA disclosures  we learned about these only through a leak. The fault with FOIA is not its breadth, but its limitations.

Most of the clamour for secrecy involves the conflation of protecting "national security" or "privacy" with preventing "political embarrassment". There is also a vicious circle: we fail to see the perils of secrecy because the secrecy laws make it almost impossible to describe the danger.

I have the privilege of a security clearance in the United States. I take my obligations under the relevant laws extremely seriously and I never violate the rules that govern my access to the prisoners that I represent in Guantánamo Bay. That said, I have been aghast over the last eight years to see the kind of drivel that is considered "classified". One example, discussed in some detail in Ian Cobain's book, and about which I can talk somewhat openly, is the case of Binyam Mohamed. Because the UK security services had indisputably been "mixed up in the wrongdoing" of Binyam's torture, the UK courts ordered that certain documents be revealed to me, as his US lawyer, to help us secure him a fair hearing. Seven paragraphs describing the bare bones of these materials were eliminated from the judges' original opinion based on the vehement objection of the British government.

Ultimately, the judges made these paragraphs public. The judgment made clear that the documents contained far greater detail of Anglo-American misconduct  details that presumably corroborated Binyam's claims of torture. Rather than hold a trial on these issues, the US shipped him back to Britain; rather than risk further embarrassing disclosures, the UK government settled Binyam's civil claim for damages.

The sequel to this episode was depressing: the coalition government has pushed forward with the euphemistic justice and security bill (more accurately called the secrecy bill). This would ensure that no such embarrassing judicial revelations ever occur again. We are told that we have no right, for example, to know how British officials worked with Colonel Gaddafi to help the ogre torture his opponents in Libya. We are told that the British public has no right to know what policy governs when the MI6 shares targeting information for the US "kill list" in Pakistan  that would be a national security issue, albeit one that involves conspiring in an international war crime.

This is where Cobain's readable book makes such a vital contribution to our evaluation of how Bush and Blair  and their heirs  have thwarted the march towards democratic openness. Cobain and I once shared the comfortable notion that Britain stood above the nastiness of torture. Cobain's book demonstrates how naive we were.

One fault of the Bush-Blair years was the politicians' failure to learn basic lessons of history: torture did not secure reliable information in 1600 (when witches "confessed"); it was no more helpful in 2001. Cobain fills in that history in a way that should be required reading for those contemplating a vote for the secrecy bill. He demonstrates a pattern that flows, sadly, throughout the 20th century and into the 21st.

During and just after the second world war, we hated and feared Germans, so we tortured them. Interrogators were told that "mental pressure but not physical torture is officially allowed." While murder was forbidden, interrogators were told they "were permitted to threaten to kill prisoners' wives and children", techniques that were deemed "quite proper". The interrogators read between the official lines, just as their counterparts did later in Guantánamo Bay and Abu Ghraib. They employed stress positions (standing up for eight days on end), strappado (hanging from the wrists, originally devised by the Spanish inquisition) and denial of food, combined with the "standard sleep deprivation and isolation regime". In a precise parallel with Bagram air base, two prisoners died in the custody of one Captain John Smith.

In the British torture prison at Bad Nenndorf, when a prisoner complained that he was going to starve, Captain Smith replied with sang froid: "Yes, it looks like you are." More than 60 years later, Cobain tracked down one German victim, a tough retired businessman, who began trembling with fear when he learned the subject of the proposed interview.

What did this systematic abuse of Germans achieve? These "interrogations  proved, beyond doubt, that Hitler was dead." When the political mandarins were faced with the horror of what had been done to the prisoners, the truth was too embarrassing to bear, so the British authorities made sure there were no public prosecutions where inconvenient truths might seep out. One witness was advised to "escape" (by walking out of the open gate) after being told that if he testified against the British officers he would be the one spending the rest of his life in prison.

Cobain's history continues with British abuses in the late colonial era. As the world sought scientific answers in the 50s and 60s, so the British sought more scientific methods of abusing prisoners in the cold war. Then came the notorious "five techniques" used on the alleged terrorists targeted in Northern Ireland before, most recently, we repeated all the mistakes of history with the "war of terror" (as Borat called it) and Iraq.

We do not, of course, yet know all the sordid details of our recent past. The security services are, with the energetic support of the government, devoted to keeping their misconduct secret for as long as possible. Cobain has used declassified materials from years gone by to demonstrate a pattern that has been recycled with the perceived terrorist threat faced by each generation. His excellent book will, I hope, educate us all.

 Clive Stafford Smith's Injustice: Life & Death in the Courtrooms of America is published by Harvill Secker.

 This article was amended on 6 December 2012, to insert the word "alleged" before "terrorists" in the penultimate paragraph.

I am not prone to gasp and nor would I describe myself as naive. But the scale of torture in the British security services, as revealed by Ian Cobain in this admirably researched book, took me aback.

Cobain, an investigative reporter at the Guardian, invites the reader to look at the post-9/11 era in a different way. The so-called war on terror may, through the rendition of suspects to secret locations and the use of Guantànamo Bay, have brought into the public consciousness the brutal activities employed by authorities in the US, UK and elsewhere. But Cobain makes it clear, with devastating effect, that these were nothing new.

The Brits have been torturing for generations. The author could have begun with the Boer war and the concentration camps that have UK copyright. Instead he starts his journey with the interrogation of German prisoners, not just during the second world war but long after it was over. "Unbeknown to the Red Cross, the British were operating interrogation centres at three internment camps, while in Berlin there was a fourth within a former Gestapo detention centre," he writes.

The retreat from empire did not take place without the odd electrode or kick where it hurts. From Yemen to Kenya to Cyprus, the British did whatever it took to hold their ground and to fend off insurgents. Torture, British-style, receives a brief dishonourable mention in Barack Obama's memoir, Dreams from My Father. His grandfather, Hussein Onyango Obama, having served in the British army in Burma during the second world war, was accused of being an insurgent. His third wife recounted how "white soldiers" "would sometimes squeeze his testicles with parallel metallic rods. They also pierced his nails and buttocks with a sharp pin, with his hands and legs tied together with his head facing down."

The further you delve into Cobain's book, the more depressed you become.

Even as their economic and strategic power waned, the British were seen as global leaders in torture techniques. "Our very simple system is admired," declared Brigadier Richard Mansfield Bremner, commandant of the British army's intelligence corps. The "five techniques" combined isolation, sensory deprivation, seemingly self-inflicted pain, exhaustion and humiliation. "It was guaranteed to leave no marks that would result in either official embarrassment or the risk of war crimes prosecutions. It would, however, cause intense pain and terror, plus lasting psychological damage."

Perhaps in those days it was easier to get away with it: deference was stronger and information was harder to come by. Even Amnesty, according to the author, was briefly happy to connive. Journalists were usually persuaded to turn a blind eye. The author valiantly sticks to the facts. But his absorbingly grim tale would have been enhanced by at least recognition of the competing arguments. That is not a call for moral relativism, but for an acknowledgement that the "do whatever it takes" argument resonates with much of the public.

Labour administrations in the UK and Democrats in the US have been as keen on extra-legal coercive methods as Conservative and Republicans. Rendition was active in the 1990s under Bill Clinton. The author points the finger at ministers and officials in the Blair and Brown governments, who knew torture was illegal, and did everything they could to keep it out of the public eye. "It was to be a dirty little secret," Cobain asserts, "known only to a select group of men and women. And if necessary, Britain's use of torture would be concealed through statements by senior political figures that were the direct opposite of the truth."

The result? Nothing much. The lack of outcry to the issues raised in Cobain's book speaks volumes.