In a telegram on November 21, 1943 Winston Churchill defined a fundamental difference between the Anglo-American way and that of our enemies. Churchill wrote: “The power of the executive to cast a man into prison without formulating any charge known to the law, and particularly to deny him the judgment of his peers, is in the highest degree odious and is the foundation of all totalitarian government whether Nazi or communist.”

Perhaps Tony Blair and George W Bush regard Churchill as a bleeding heart leftie. But what Churchill’s view represents is an old basic principle of Anglo-American warfare and justice: fight war with ferocity but never lose your democratic soul and always treat prisoners humanely.

This is never an easy balance, of course. In the fog of conflict we make mistakes. Executives invariably overreach in prosecuting wars and have done so in both America and Britain (the Guardian claimed yesterday that SS prisoners were tortured at a secret London centre).

Our system — of habeas corpus, executive powers subject to legislative and judicial checks, and free speech to air the issues — is specifically designed to correct such errors. That is its beauty — and its strength. It gives us a flexibility in war that dictators lack. It makes our war-making more, not less, effective. At its deepest level, it is what distinguishes us from Saddam Hussein, the Taliban and the Islamist bombers we face today, just as it distinguished us from the Nazis and communists.

Those of us who believe in fighting the war on terror need not regard civil liberties as somehow a sign of unseriousness in wartime. Protecting liberty at home is critical to winning the wider conflict, especially in the larger battle of ideas that will ensure ultimate victory or defeat.

There is now little doubt left that the executive branches in both countries have overreached. The case against Bush, however, is far stronger than that against Blair; and it begins with the legal sanctioning of torture and the abuse of military detainees.

Advocates of abuse insist that Al-Qaeda members are not signatories to the Geneva conventions and so do not merit humane treatment. The argument misses the point. This is not about terrorists and their barbarism. It is about us and our civilisation. You cannot fight a war to bring democracy to Iraq and Afghanistan while torturing detained insurgents in Saddam’s prisons and makeshift camps in the Afghan wilderness. As a policy it is incoherent, damaging to our cause, immoral and ineffective.

The confessions you get from individuals broken by mental or physical brutality are highly unreliable, as any professional interrogator will tell you. It harms the torturers as much as the tortured, which is why much of the resistance is now coming from the ranks of the CIA and the military charged with this vile practice. If Israel eschews the tactic, so can the United States. The price that the West has paid in terms of moral standing is already incalculable.

The same goes for the notion that the executive needs no checks in wartime. The legal architects of Bush’s policy have argued that the president as commander-in-chief has constitutional powers that allow him to circumvent laws and treaties as he sees fit in wartime. This radical new extension of presidential power is neither conservative nor effective.

Unchecked executive power has made terrible mistakes in the occupation of Iraq. Secrecy and paranoia have helped to compound these errors rather than rectify them. Congressional trust and blank cheques were misplaced. The president’s sad attempts to explain a misguided policy shrouded in secrecy have only undermined his credibility.

Last week, for example, the president insisted that “we do not torture”. It was a bold statement. It is also patently untrue. Last week, for example, we discovered that the CIA operates several “black sites” for terror suspects in former Soviet camps in eastern Europe. Among the techniques authorised for the CIA to use against them is “water-boarding”, where inmates are plunged or drenched in water to the point of drowning. This is repeated until a confession is forced.

According to a Pentagon commissioned report, this technique was used on one detainee in Guantanamo on 17 occasions in one month and was still legally not “torture”, according to Bush administration lawyers. Hence the president’s carefully parsed statement. His strained legal definition is as absurd as his predecessor Bill Clinton’s definition of what constituted “sexual relations” with Monica Lewinsky. And it is of infinitely graver moral import.

Free speech? In America the first amendment protects it. But the investigation that indicted “Scooter” Libby, chief of staff to Dick Cheney, the vice-president, has chilled the press’s ability to uncover secret policies that the government does not want us to know in ways that we may come to regret.