There are "some people so famous, so much the focus of media attention and public conversation, that they cease to be viewed by many as human beings. Britney has joined them." Alastair Campbell's point applies to anyone who is recognisable to the general public by their first name.

At the time, he was worried that Tony and Cherie had achieved this non-human status. Now, it applies to Gordon. The Prime Minister is already into the chicken-house phenomenon, which hit Tony Blair in his eighth year as Prime Minister. When I worked in a chicken shed, one of our jobs was debeaking the birds, cutting off the tips of their beaks to stop them pecking each other. If this weren't done often enough, the overcrowded chickens would draw blood – and when a spot of blood showed, the other birds would peck until its guts were spilled.

I thought Blair was looking bloody in 2004. I remember Gordon Prentice (Lab, Troublemaker Central) asking him in the Commons that October if he could think of "a single dramatic act of renewal that would make the British public sit up and take notice". He meant resign, a coded offensiveness that not even Frank Field has yet attempted on Blair's successor. In the face of this broiler madness, it was an extraordinary achievement on Blair's part not only to win the general election – with Gordon Brown's help, for the benefit of those sour critics who say that Brown has never won a democratic mandate – but to stay on for a further two years after that.

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It must be doubted whether Brown has that sort of regenerative capacity. Our opinion poll today won't help. It finds that 57 per cent of respondents – and 43 per cent of Labour voters – agree that "the Labour Party has to change leader if it is to have a chance of winning the next election". Yet it is worth standing back for a moment to wonder at the ferocity of the contempt that Brown already invites, and which will surely hand the Conservatives this week their first by-election seat won from Labour since Mitcham and Morden in 1982. (And that was a special case. Whenever an MP defects to another party, they are asked, "Why don't you stand down and fight a by-election in your true colours?" To which the honest answer is: "Because of what happened to Bruce Douglas-Mann in Mitcham and Morden." He defected to the SDP, did the honourable thing, and lost to Angela Rumbold.)

Plainly, Brown has not performed brilliantly as Prime Minister. But then, he has not done much wrong either. He is being compared to Anthony Eden, who made a misjudgement of Suez that served the nation badly and lied about it in the Commons. Or to John Major, who presided over drift at home and appeasement in the Balkans. Neither comparison is remotely fair – at least, not yet.

It is true that Blairite ultras, such as me, have long expounded the view, ascribed to Blair by Lord Levy, that Brown could not win against David Cameron. But I hope that I have always focused on Brown's judgements rather than his personality. I have given him credit for the handling of Northern Rock, for example, which Cameron would have done no better. I feel completely at odds with the air of anger and vindictiveness towards Brown that seems to hang over the voters of Crewe and parts of the media. The fury over the scrapping of the 10p tax rate is out of all proportion to the numbers of losers and the amount they have lost. It was a symbol of other resentments, which is why it was unassuaged – as our poll also finds – by last week's tax changes, from which 22 million people gain.

The pool of anti-politician sentiment in this country can be both reflected and magnified by the increasingly short-cycle, high-opinionated media. This is a problem that goes beyond the personality and leadership qualities of Brown. Although the Brownite ultras were contemptuous at the time, they should have listened more carefully when Blair made a speech criticising the media just before he stood down. Blair had identified a problem. It sounded petulant, inevitably, and the analysis was shallow: "Today's media, more than ever before, hunts in a pack. In these modes it is like a feral beast, just tearing people and reputations to bits." He was also cowardly to name only The Independent as an example, when, as Alastair Campbell confirmed later, the real target was the Daily Mail.

Yet he was on to something, and Brown now finds himself on the receiving end of that very something. The media-voter feedback loop has become overwhelmingly negative. The BBC is the measure of this, the weathervane. It was not just John Humphrys, whose incivility on the Today programme seemed designed (unsuccessfully) to provoke the temper that has been written about but never seen in public. Other, less obviously calculated slights last week included the close-up of Brown's bitten and ink-stained fingers on the 10 o'clock news, and the shot on Newsnight of the Prime Minister snapping from one fixed grin to another when a producer clapped.

If the BBC is a pointer, pretending not to be in the fight, the real beasts are the newspapers. Brown faces a toxic combination of Rupert Murdoch and the Mail group, both of whom are playing with him, and The Guardian, whose columnists are bitter at his failure to be Clement Attlee. The Sun endorsed Boris Johnson for Mayor of London, a trial run for a switch to the Conservatives nationally at some point in the next two years. Paul Dacre, the editor of the Mail, continues to maintain cordial personal relations with the Prime Minister, but these have decreasingly little effect in restraining the anti-Labour tone of his newspaper.

If Brown is brought down by the frenzied, pecking chickens, how long will the next leader last? Brown was given the benefit of the doubt for three months before the beaks started to come for him. Plainly, some politicians can survive against this relentless media culture longer than others. Blair, it should be remembered, had a broadly favourable press for eight years (1994 to 2002) and then survived for another five. Barack Obama has enjoyed even more extravagantly messianic delusions – not his own, but those projected on him by the media. But Cameron, or David Miliband, or James Purnell? How long would they last? As Campbell said of the treatment of Britney, Diana, Madeleine and Beckham: "Perhaps the phenomenon is beyond healing."