Cruel Britannia: A Secret History of Torture, By Ian Cobain

This admirable investigation into torture in the fraying empire will overturn myths

Legal bans on torture in England, then Britain, go almost as far back as written law itself. It was supposedly forbidden even in medieval times, while modern prohibition can be traced to a law of 1640. But for just as long, governments have in reality allowed it, practised it, and lied about it. Almost always, the open or tacit plea has been that of "exceptional circumstances", plusword games over definition. When does "forceful questioning" or uncomfortable confinement shade into torture?

It reminds one of the powerfully suggestive notion – first proposed by German legal theorist (and ardent Nazi) Carl Schmitt, latterly developed by Italian philosopher Giorgio Agamben – that the very foundation of modern state power lies precisely in the capacity to define what is "the exception". Making exceptions is the norm. One recalls that even 17th-century witchfinders like the infamous Matthew Hopkins usually did nothing more obviously violent than deprive their hapless victims of sleep. That was quite enough to induce hundreds of false, absurd confessions and carry their makers to the gallows.

Guardian investigator Ian Cobain begins his story with the Second World War, but could easily have gone much further back. A horribly repetitive picture would emerge: of British governments and their agents using systematic brutality against ever-changing categories of opponent, bending and twisting the law, and then lying about it all. His expose prompts a third historical reminder: that if British self-images and stereotypes of national character revolve around ideas of decency and fairness, a strikingly persistent feature of others' images of Britishness has been the charge of endemic hypocrisy.

Cobain's case that torture was a frequent, even routine thing in 1939-1945 Britain, especially in secret interrogation centres like the "London Cage" in Kensington (now, perhaps ironically, the Russian Embassy), rests more on inference and suspicion than direct hard evidence. Soon after, though, that changes: it's clear that in postwar Germany, at the Bad Nenndorf camp and probably elsewhere, there was constant horrific maltreatment. It's quite unsurprising to learn that its victims, initially mostly suspected Nazi war criminals, very soon became alleged or possible Communist agents.

The main scenes of torture then shifted to multiple sites of decolonisation and anti-colonial insurgency across the globe. Of these, Kenya's Mau Mau war has recently received the most attention: indeed, the present British government has now formally admitted that suspected rebels were tortured. But there is accumulating evidence of similar behaviour almost everywhere that the declining empire faced violent challenge: in Palestine, Malaya, Cyprus, Aden, plus, after the end of formal imperial control, Dhofar, Borneo and more.

Crudely but fairly accurately, it can be said that the darker the skins of the rebels, the worse the British official repression. Military historians and counter-insurgency experts continue to debate whether Britain pursued a distinctive "minimum force" doctrine in its 20th-century small wars. But even if so, it's ever harder to sustain the conventional wisdom that – unlike the French – British late-colonial torture was not widespread or routine.

Cobain's account becomes again more focused and detailed when he turns to Northern Ireland in the 1970s and after. There, the notorious "five techniques" of isolation, sensory deprivation, exhaustion, humiliation and seemingly self-inflicted pain were perfected. They left no obvious physical marks, and officialdom long tried to argue that they could not be defined as torture at all, but were calculated to cause intense suffering, terror and enduring psychological damage.

And in the "war on terror", while UK state agents do not, supposedly, use those techniques they rely on, facilitate, and encourage other countries' jailers who do, and who learnt them from us. Ministers and officials in the Blair and Brown governments, Cobain shows beyond reasonable doubt, knew all about this, knew it was illegal, and worked shamefully hard to conceal and deny it.

Investigative journalism and media whistleblowing in Britain have taken some very hard knocks in recent weeks. Cobain's work does much to sustain those trades' honour and underline their necessity. He offers a dramatic challenge to official dishonesty and public complacency, past and present. Perhaps the most disconcerting thing of all, though, is that in some respects – especially the end-of-empire story – he has still only scratched the surface.

Stephen Howe is professor of the history and culture of colonialism at Bristol University