At a cursory glance, it may seem that the British court's decision in Binyam Mohamed's case yesterday reached a horrifying result: the evidence of Binyam's torture will be kept secret.

The judges emphasised that there is a "very considerable public interest in making the [proof of abuse] public, particularly given the constitutional importance of the prohibition against torture". Despite this, they ruled that the foreign secretary has the power to suppress the evidence by claiming "national security".

Yet the judgment is canny. If the judges had ordered the material to be revealed, over the government's objection, there would have been a protracted appeal and nobody would have learned anything for months or years. Instead, they have placed both the British government and the Obama administration in the immediate and uncomfortable position of having to confess whether they want to cover up evidence of torture.

A little background: Binyam, the Guantánamo prisoner represented for years by Reprieve, has described how he was abused in Pakistan, then rendered to Morocco where a razor blade was taken to his genitals. We know - from the judgment - that the UK has documents authored by the Americans themselves that would help prove some of his mistreatment.

I have seen this evidence, as I have a security clearance in the US. You can't see it. Why not?

The judges repeat no fewer than eight times that the Bush administration threatened the British that if the judges made this evidence public, the US would retaliate with sanctions.

Since when do friends level threats at friends to prevent them from revealing evidence of crimes? To be sure, in The Godfather, the mafia might have threatened to put some cement shoes on an informer, but one hardly expects the same approach to be taken by the White House.

In this case, there are a multitude of crimes that have been committed. The first was the torture. The second, the failure to reveal it. These threats represent a third independent offence - an attempt to blackmail the British into hiding evidence that they have a legal duty to reveal. And, because the British apparently have jelly for a backbone, the threats have worked. The judges were shocked:

We did not consider that a democracy governed by the rule of law [the US] would expect a court in another democracy [the UK] to suppress ... evidence contained in reports by its own officials ... where the evidence was relevant to allegations of torture ... politically embarrassing though it might be.

The British government led the court to believe that the Obama administration has adopted the same line as its predecessor. But is this really true? Certainly, President Obama needs to speak for himself.

Indeed, the judges conclude with something close to a plea for common sense: "It must now be for the United States government to consider changing its position or itself putting that information into the public domain."

When history reviews the past eight years, the most lasting concern will not be ill-advised experiments such at Guantánamo Bay. Rather, it will be the creeping tendency of democratic governments to use "national security" as an excuse to keep the truth from those who have elected them. After all, if the US and the UK can conspire to suppress evidence of torture, what other dark secrets can they hide?

Clive Stafford Smith is the founder of Reprieve and has spent 25 years working on behalf of defendants facing the death penalty in the USA.

more Clive Stafford Smith