Gordon gets lucky - but has he got the It factor?

Mr Brown, the New Puritan of No 10, eschewed all that and went for a short and homely speech on the doorstep, reproducing the motto of his old school in Kirkcaldy: "I will try my utmost." He has, of course, tried his utmost to get here, as Mr Blair, departing earlier than he would have wished, could tell us.

As for the old tension of whether a political successor should stress continuity or change, there was no doubt today. "The old politics," said Mr Brown, was no longer up to delivering what people want. The "work of change" would begin straight away. This is code for co-opting some cross-party support and possibly ministerial roles in his first reshuffle.

But it is also sends a broader message — the Blair years are over: long live Gordon Brown. The old argument between Labour strategists about continuity versus change has been resolved early and decisively in favour of change.

That also provides Mr Brown with a lasting conundrum: how to explain why the government in which he served was on the wrong path and what exactly does he want to change anyway? He is well aware of these tensions, but then you do not wait 10 years to become leader in order to continue as the other guy did.

Especially not if you are Gordon.

This was a sober, almost solemn beginning.

But for Mr Brown the early omens are good.

The new leader could not have wished for a better house-warming present: a Tory defection nicely timed for the eve of his arrival in No 10. Quentin Davies, member for the historic Thatcher shrine of Grantham, high-earning City consultant on the side and veteran of two former shadow cabinets, garlanded the Labour benches at Prime Minister's Questions, an unfamiliar florid figure.

It is the only way a member of Brooks's and the Beefsteak is going to get on in the Labour Party.

Contrary to what parties say at the time, defections matter because they represent a flow of belief and hope from one direction to another.

That is what happened when Baroness Nicholson went from the Tories under John Major to the Lib-Dems and deepened the crisis of faith inside the party, and again when Shaun Woodward decided he preferred Mr Blair's company to his old tribe.

The traffic was supposed to be going in the other direction by now. For some time, David Cameron has hinted at attracting major figures from the other parties — since he, too, has staked his claim boldly on a less off-putting, more inclusive party open to those beyond the traditional core. He needs converts to prove it, not absconders from Camp Cameron. Two peers departing for UKIP could be dismissed as a shake-out of the old guard. This cannot, and Mr Cameron, generously rising to applaud Mr Blair while his party sat in sullen mood grouching about Europe, looks more and more at odds with the benches behind him.

More damaging than the loss of the MP himself are the terms of his denunciation of his party..

The point about his parting shots about the Tories' leadership's lack of direction and substance is not whether they are fair or not. It is whether they strike a chord. Of course, Mr Davies misses out his old leader's great strengths: that he is likeable, charming and has engaged public interest in the Conservative Party for the first time in a decade. Added to which, he is comfortable with the pickand-mix politics and social beliefs of the post-millennium era in a way that challenges the more stolid — some might say dated — Mr Brown.

His problem is that he has not yet successfully persuaded his party to join him in the awfully big adventure of crafting a new approach to accompany his stylistic repositioning. His own inconsistency and mistakes of political management are becoming harder to ignore. The grammar schools debacle was badly handled in terms of raw politics.

Mr Brown's decision to back academies — better late than never — has confounded the Opposition, which is preoccupied, to the point of obsession, by hatred of the new Labour leader, while not quite getting the measure of him. Now he has a new opportunity, and his approach and emphasis must change too.

He has his own rocky road ahead: Mr Brown must ensure that talking of change — which will delight those glad to see the back of Mr Blair — does not morph into a rejection of the Blairite grip on the realities of electoral politics and the centre ground, a combination which proved extraordinarily durable.

It is fashionable to dismiss Mr Blair's domestic legacy as incomplete or crumbling, but that underestimates his main achievement. On one pretty major score, he deserves a resounding pat on the back. He is the Labour leader who dragged his party away from its belief in the state as automatically the best way to deliver public services.

He had the vision to make changes against the grain of opinion and instinct of his party and fight for them — often in the teeth of resistance from one Gordon Brown. Well tempora mutantur, as Mr Davies might well agree next time he sits down at the Beefsteak.

The Conservative Party today is the clearest testament to the vast impact of Mr Blair on British politics. He is the reason it has been unable to recover its confidence or its claim to the centre ground for so long. His example is why Mr Cameron, and not a more traditional contender, persuaded its grassroots that it needed a new kind of leader, and he is why the shadow chancellor, George Osborne, who upset the dinosaurs again by evoking the "heir to Blair" idea, is diagnostically right. Mr Blair's ghost hovers over the Cameron Tory Party, wishing him luck, even if he can never say so.

Today he is gone to the political afterlife, and Mr Cameron is about to feel the Brown juggernaut descend.

The new leader still contends with a kind of uncertainty that has hovered over his journey to No 10. "He'll do a really good job," said one longstanding friend last week, and then, anxiously, "but will people go towards him?" It's not the kind of question that ever haunted Mr Blair. We just knew that the voters would "go towards him" — and through thick and thin, they did.

We have taken a lot for granted. Now we'll see whether Gordon, lucky at last, has the It factor of his own..