A reader who followed this column throughout the Blair years would know that I always thought Tony Blair was a fraud. But I have less often remarked that he usually seemed a rather pleasant person: unvindictive, and often generous about others.

He was not instinctively partisan. Joining in the yah-boo stuff as the Commons required, he seldom had his heart in it. Tribe, doctrine and debate didn't really interest him, he was barely capable of grasping general principles, and there wasn't an ideological bone in his body. He shafted people cheerfully when it suited him but rarely got angry or bitter about the reasons. Strong beliefs, a conscience and staunch personal loyalties twist and embitter us; they get us all wound up.

Mr Blair had the sunny good nature of the truly selfish man.

Gordon Brown has the internally curdled nastiness of a truly public-spirited man. Here is a politician to whom struggle in a great and deep national purpose - though that purpose is tangled, paranoid and conflicted beyond coherence or hope - means everything. It is his life.

Riches, houses, cars, status, foreign holidays... personal happiness itself, are almost nothing to him. He is, in that sense, selfless. It makes him shockingly disagreeable. On Planet Tony all was for the best in a best possible world. On Planet Gordon ill nature rules and monsters roam.

So there has been, since Mr Blair left, a profound change in the political atmosphere, and it was very marked at Labour's conference in Manchester. Though calm, the air was weirdly sulphurous. Mr Brown engenders and embodies a new rancour - a bitter, personal, raving dislike of the Conservative Party and its leadership.

“They want us to believe,” he said on Tuesday, “that, like us, they now care about public services... They want to tell us we're all progressives now... they want to tell us they now believe in investing in education... [but] yes friends, they would even take away Sure Start from infants and their parents... If you look beneath the surface, you'll see that the Conservatives might have changed their tune, but they haven't changed their minds...”

And this all came after a passage in which he accused David Cameron of “serving up” his children “like props” for media cameras. From a man who had become the first British party leader to use his wife to introduce him on stage, and who, to the distaste of even Alastair Campbell, writing in his diary, had invited a friendly newspaper editor to the funeral of his own baby, this could be seen as hypocrisy of the most cynical sort; and that's how many Tories will see it.

But I don't think it was. Mr Brown honestly believes that the Tory leadership is wicked, and cares nothing for the rest of Britain. Everything the Tories do is then interpreted in this light. His own actions (he thinks) should be seen differently, as his intentions are good.

How should the Tories respond, gathering as they are today for their own conference in Birmingham?

Quite early on in Mr Cameron's leadership I was one of those who advocated a no-holds-barred Tory attack, arguing that Mr Brown was a weak and flawed leader and that the Opposition needed to ram this home, again and again, and mercilessly. It's not for me to judge whether this approach has been appropriate or successful, but I have never had a moment's doubt because I am sure that Mr Brown is bad not just for Britain but for the British centre Left.

And this confrontational approach is more or less what the Tories have adopted, I think to good effect: such good effect that, taken with on-the-record and off-the-record attacks on Mr Brown from his own colleagues, the damage that his reputation has sustained is almost certainly beyond repair.

So should the assault continue? After Manchester I have concluded that there is a strong chance Mr Brown will be our Prime Minister until 2010. David Miliband's potential Heseltine moment was more a Portillo moment and I fear he's done for. James Purnell is unknown and unready (interestingly, the Work and Pensions Secretary argued at the Times fringe meeting in Manchester that impugning the Tories' motives was the wrong tactic: Mr Brown then adopted it).

The repeated insistence of the Health Secretary, Alan Johnson, that he doesn't want to lead Labour may have to be taken at face value. And the popular leftwinger Jon Cruddas is a sufficiently dangerous wild card to make Blairites think twice about triggering a leadership contest in the first place. So Labour may end up with the worst of all worlds: a damaged, disliked - and irremovable - leader.

Tough for Labour. But this figure also happens to be our Prime Minister, and at a seriously nervy time for world affairs, global finance and our domestic economy. And there is more than a year to go.

So I'm beginning to wonder whether at this time, when Mr Brown's defects are now so universally known, that an opposition team readying itself for government should be taking further kicks at what Vince Cable, the Liberal Democrats' treasury spokesman, called “the twitching corpse” of the Prime Minister.

It may begin to look sadistic, irresponsible, lazy. It might not seem to rise to the gravity of the mess we're in. For Conservatives it could be counter-productive. Instead, a display of high-mindedness and good nature might better confound their enemy and impress the public.

So instead of trading insults, maybe they should respond with mild disappointment, sorrow not anger, and impeccable courtesy. They might accept in Mr Brown and his team a good faith that he is unwilling to accord to them. They should refer back to the PM programme on Radio4 after Mr Brown's speech on Tuesday. A focus group of Stafford voters sat through the speech, keying in their positive or negative responses throughout, on a scale of one to five. Mr Brown scored mostly fours, and the final verdict sounded, on balance, positive. But whenever (and only when) he returned to his very personal attacks on the Tories, the ratings dipped.

Name-calling irritates voters, even though, when it strikes a chord, it may shift attitudes. But more importantly, most floating voters don't think David Cameron is a nasty person or a lying extremist. Mr Cameron might ponder that good opinion, and take care not to disturb it by seeming to bully a broken Prime Minister.

Few have got more often beneath the skin of incompetent ministers than Michael Gove, the Shadow Schools Secretary. None has been more consistently polite. Now that the early Brown onslaught has been utterly routed, and their adversary is lying wounded on the battlefield, waiting to be bayoneted by a general election, Mr Gove's colleagues, too, might consider studied courtesy, sceptical inquiry and a hint of sarcasm, as their next weapon.

A Tory show of despairing good manners towards Gordon Brown may prove the winning strategy for what begins this autumn: the endgame.

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