Mr Blair must face the critics with little help from his American friend

Tony Blair's special relationship with George Bush looks even more of a one-way affair now. The Americans have not exactly been helpful to their "First Friend" in the past week.

First, President Bush designated the first six detainees held at Guantanamo Bay for trial, and - ignoring British unease mumblingly expressed over the past 18 months - two of them are Britons. Then Mr Bush allowed his spokesman, Ari Fleischer, to say that the British story about Iraq trying to buy uranium from Niger was so dodgy it should not have been included in a presidential speech. Finally, Donald Rumsfeld, the US Defence Secretary, tactlessly repeated his view that the threat from Saddam Hussein had not increased - it was only that 11 September changed US perceptions.

Thanks a bunch, Mr Blair must be thinking. Alone among world leaders, he ordered his nation's troops into battle alongside the Americans in Iraq. He threw away his ambition to lead the European Union and took a desperate risk with his party and his people. And all for what? Grateful many Americans are - the award of a Congressional medal will be a token of that - but now the imperatives of the US electoral cycle are reimposing themselves. With many leading Democrats looking to unpick the arguments for war in much the same way that they have been unpicked in Britain, Mr Bush is going to defend himself without sentiment.

He is not too aware, it must be suspected, of the offence caused to British patriotism by the fact that US citizens are exempt from the special military justice at Guantanamo Bay, while British citizens are not.

That insult has prompted the Daily Mail to join many MPs in calling for the Britons to be sent back and tried here. And the Prime Minister may hope to gain some concessions before or during his visit to the President next week. Whether or not he does is, frankly, beside the point. Unless all the 600-plus detainees at Guantanamo Bay are tried - as the Prime Minister said - "in accordance with proper canons of law so that a fair trial takes place and is seen to take place", the moral standing of the US is undermined. It is no more justifiable for Britons and Americans to be exempt from the kangaroo commissions than for Americans alone.

Despite the slight toughening of British ministerial language over the past week, it seems impossible that the peculiar form of justice that is still being thought up by the Pentagon could ever be, or be seen as, a fair trial.

It is enough to know that the United States will not allow the detainees the protections of its own constitution or of any other basic human rights law. The European Convention, for example, includes the right for any detainee to be "informed promptly of the reasons for his arrest and of any charge against him".

The US will not even grant the detainees the status of prisoners of war, which might allow international courts to decide that the limited rights to choose their own lawyers was in breach of the 1929 Geneva Convention.

Mr Blair knows he is on weak ground. When Charles Kennedy asked - in a reasonable, conversational tone - what Guantanamo justice said "for British influence, which he heralds, over the Americans", the House of Commons was uncharacteristically silent.

The Prime Minister must know, as the clamour grows for an independent inquiry into the decision to go to war in Iraq, that his slavish support of America - right or wrong - presents him with the most dangerous moment of his premiership so far.