Leading article: Did Mr Straw really see no evil?

No one in a position of authority in any modern democracy says that he or she tolerates the use of torture. Indeed, no one in a position of authority in any country would say such a thing. The UN Convention Against Torture has been signed by 76 nations – yet many of them are not regarded by the independent British judicial system as being safe for the return of refugees.

In the case of Binyam Mohamed, the British resident who has returned to this country from Guantanamo Bay, the Convention provided no protection. There can be no reasonable doubt that he was tortured in Afghanistan, Morocco and the US naval base at Guantanamo which, the US Supreme Court ruled, is subject to US legal jurisdiction. All three countries are signatories to the Convention.

Afghanistan and Morocco are one thing. But before 2001, higher standards were expected of rich liberal democracies such as the US or Britain. We, the citizens of these fortunate nations, and even most of our politicians, seriously believed that our governments could have nothing to do with such abhorrent and ineffective methods. But that, as the experience of the past seven and a half years has shown, was not enough to prevent people being tortured by, for or on behalf of the governments of those same liberal democracies.

Mr Mohamed's case is currently the most vivid example of the moral void into which the US government fell after 9/11, and with which our government was complicit. We defy anyone to deny that an appalling injustice has occurred, in which British intelligence services played a shameful role.

After 9/11, President Bush dismantled America's moral authority by redefining torture to exclude "enhanced interrogation techniques" such as simulated drowning or waterboarding. The message was sent through the military hierarchy that the US constitution and international treaties were constraints to be worked round rather than the principles they were defending.

The British Government did not go so far. Tony Blair and Jack Straw did not like Guantanamo, but said so quietly; they adhered to a definition of torture that respected the meaning of words; and they said that Britain would have nothing to do with it. However, Mr Straw as Foreign Secretary showed a lack of curiosity – to put it generously – about what British and US security services were up to. Official statements about the practice of flying detainees around the world to be kept in CIA prisons or to be tortured in other countries were offhand, incomplete and misleading.

Mr Straw was in post when British spies were supplying the questions to Mr Mohamed's Moroccan interrogators.

That case is only the most dreadful of many instances where the British government's policy seems to have been to turn a blind eye. This was not simply a moral and legal failing but a practical one: they should have known that any information extracted under duress would be worthless. Mr Mohamed's story illustrates that point very clearly.

It is a case study in the folly of the "hard" approach to this issue. It can be tempting, even for The Independent on Sunday, to think that many or even most of the US detainees were up to no good. It is possible that Mr Mohamed's reasons for being in Afghanistan on a false passport were not as naive as he suggests. But torturing him destroyed the value of any intelligence that he might have had.

David Miliband, the present Foreign Secretary, has the potential to hold somewhat higher moral ground, not least because these lessons have been (re)learnt. Indeed, his role in the Mohamed case has been widely misunderstood. He ensured that Mr Mohamed's lawyers were given intelligence material to help prove he was tortured; his dispute with the courts was over how much of it could be made public.

There is hope on both sides of the Atlantic now that it will be understood at all levels that torture is not simply morally wrong but practically counterproductive.

President Barack Obama gave the right lead from the top in his address to the joint session of Congress last month: "To overcome extremism, we must also be vigilant in upholding the values our troops defend," he said. "And that is why I can stand here tonight and say without exception or equivocation that the United States of America does not torture."

He must make sure that the US military and security services know that he means it. And Mr Miliband must eliminate any equivocation in Britain's supporting role. That would be a special relationship we can believe in.