Charles Clarke’s deft political touch might have deserted him when he was Home Secretary, but as the interviews he has given this week have shown, he has certainly regained it.

His remarks were calculated, clinical and effective. He has achieved both his aims.

First, he has settled his score with his successor, John Reid, for badmouthing Mr Clarke’s performance as Home Secretary. Mr Clarke accused Dr Reid of jumping on media bandwagons and being wrong to criticise his own civil servants.

Both men are past masters at political street fighting, and the former Home Secretary has made it clear that he will give back as good as he gets.

But the real interest in Mr Clarke’s words lie in what he said about the Prime Minister: “What we are lacking at the moment is a sense of leadership and direction”.

The importance of those words lies not so much in what they say, as who has said them.

The likes of Frank Dobson, Clare Short and the other usual suspects call for Tony Blair to go morning, noon and night. It would be more noteworthy if any of them one day uttered a word of praise for the Prime Minister. Mr Clarke is very different. Loyalty to the leadership runs through his very core. That is why his words are so explosive.

They show the extent of Mr Blair’s weakness, because they show that even the moderate, centre of the Labour Party now regards the Prime Minister as politically a dead man walking.

Some have compared Mr Clarke’s words with Lord Howe’s torpedoing of Margaret Thatcher’s premiership. They are wrong. When Lord Howe called on “others [by which he meant Michael Heseltine] to consider their own response to the tragic conflict of loyalties with which I have myself wrestled for perhaps too long", he was signalling the beginning of the end for Baroness Thatcher.

She might have been unpopular, and her party might have wanted rid of her, but she remained a political colossus, and the dominant figure in the government. It was only when Lord Howe opened his mouth that the end became nigh.

The circumstances today are very different. Mr Blair was finished long before Mr Clarke opened his mouth. It has been a matter of when, not if, he departs ever since he announced that the 2005 election would be his last.

The fact that Mr Blair won a third election is now little more than a technical curiosity, since he has been utterly impotent as a political leader since that victory, unable to legislate as he would wish and unable even to direct the Government as he would wish.

But none of that makes Mr Clarke’s remarks any less damaging. The fact that it is Charles Clarke speaking out makes his words far more potent than if they had come from other lips.

Until May, when Tony Blair sacked Mr Clarke in the wake of the foreign prisoners fiasco, he was one of the Prime Minister’s strongest supporters.

There is now no rational reason why Tony Blair remains in office. Powerless to implement reforms, he is reduced to traipsing across the country making speeches about what his Government ought to have done.

Equally, however, events can develop a momentum of their own, and words can have an impact beyond their immediate meaning.

Stripped of all context, Charles Clarke has merely stated the obvious. But the context matters. This statement of the obvious, because it is made by Mr Clarke, might well hasten Mr Blair’s demise.