And, finally, truth is told about power. For many weeks now this newspaper has been decrying Gordon Brown’s Government as directionless, obsessed by the drawing of tribal dividing lines and empty of apparent purpose or ideas for the future. We have implored members of the Cabinet to acknowledge the truth that was staring them in the face. Their situation had deteriorated rapidly, to the point where they had a duty to act, not just in the interests of their own party, but of the country as a whole. Finally, someone dared. James Purnell, the Work and Pensions Secretary, take a bow.

It is no small act of political courage to stand apart from one’s colleagues as Mr Purnell has now done. Whatever else follows from his resignation, it is undeniable that in this single act he becomes one of the most significant of the talented Labour politicians of his generation. Whatever his intentions for the future, and they are not said to include a desire to lead his party, he will now always be the man who dared. When the truth so desperately needed stating, that is a laurel that he should be proud to wear.

Mr Purnell has now opened the floodgates and there is no excuse for anyone else declining to rush through. Or rather: the question has now been put. If the rest of the Cabinet, and the influential backbench MPs who are said to be collecting signatures for a leadership challenge, now decide not to follow, then they have settled on their choice for the next general election. They will have chosen to uphold a prime minister whose authority in his party is questionable and whose authority in the country is spent.

The Prime Minister is, without question, a formidable politician and a man with admirable intentions. He has tackled some of the big issues of the day with extraordinary intelligence and courage. Mr Brown has led the world through a global financial crisis. Through weeks and months of complaints and criticism he has also shown an adamantine will to survive. He has had the support throughout of a thoughtful and impressive wife and together they have brought up a young family. There is no question that Mr Brown is a man of substance.

But, unfortunately, even those qualities are not enough. The manifest deficiency that Mr Purnell has identified in the Prime Minister’s leadership will not simply go away if the Labour Party chooses to avert its gaze. In the autumn of 2007, Mr Brown’s stated reason for not calling a general election was that he wanted more time to set out his vision for the nation. Nearly two years later, we are really none the wiser. From the start of his premiership to what is increasingly looking like the end, it has never been clear why he wanted the job.

Mr Brown has also been cruelly exposed, in David Cameron’s resonant phrase, as “an analog politician in a digital age”. Accustomed to hunkering down in the Treasury, taking issues one at a time, poring over the documentation until every conceivable angle has been covered, Mr Brown has found the pace of being Prime Minister too much.

As his fortunes have waned he has turned back to the political machine that put him in Downing Street in the first place, and the aggression and bullying that has, for a long time, been a hallmark of his inner circle has spilt damagingly into the open.

But perhaps not for much longer. A terrible prospect is now in view for the Labour Party. If the Prime Minister limps on now, mortally wounded but exhaling his last through gritted teeth, the Government will relinquish its last opportunity to regain the attention, let alone the allegiance, of the electorate. The end is not yet nigh but the die is surely cast.