John Rentoul: Brown isn't working – and Labour has itself to blame

Only a handful of Blairites had the courage to oppose Gordon Brown's accession to No 10 last year, and now, even sooner than they expected, the Prime Minister has lost the confidence of his MPs. His early departure is no longer an if, but a when and a how

I would name the guilty men and women, but there are rather a lot of them. It would take up most of this column. One year ago, 313 Labour MPs nominated Gordon Brown to be leader of the Labour Party. Tony Blair, John Reid, Alan Milburn and Tessa Jowell are all to blame for the crisis in which the Government now finds itself. In fact, they are more to blame than those MPs who nominated Brown sincerely believing that he would be a good Prime Minister.

Let me instead name the seven brave MPs who told it like it was. Charles Clarke, Jim Dowd, Frank Field, Kate Hoey, Peter Kilfoyle, Siobhain McDonagh and David Winnick. They nominated neither Brown nor one of the hard-left, would-be candidates, John McDonnell and Michael Meacher. Their consciences are clear. They cannot be blamed for the disaster of the Crewe by-election, a personal and terminal rebuff for Brown.

It is no use those who did choose Brown, but kept their fingers crossed, saying that they told us so. Blair himself faced both ways, saving his endorsement of Brown until the last minute and phrasing it in the least enthusiastic terms compatible with good manners. It was no good John Hutton telling Nick Robinson, the political editor of the BBC, unattributably, that Gordon would be "an effing disaster as prime minister". He gains nothing now by being proved right. It was a pointless act of coded rebellion for Jim Murphy (Europe minister), Pat McFadden (employment minister) and Greg Pope (former whip) to be the last to nominate Brown.

What we needed, 12 months ago, was a candidate. But neither John Reid nor David Miliband was willing to stand. I thought they served their party and their country badly at the time, although I think I know why they didn't run. They thought they wouldn't be able to get the 45 signatures from MPs to put their name on the ballot paper. That would have been humiliating. So Reid folded his tent instead. Last week he was on the Today programme saying, "I have no doubt that if and when Gordon moves on it will be of his own volition." He was talking about Gordon Strachan, who has just led Reid's team, Celtic, to their third consecutive Scottish championship. Very funny. Miliband decided to wait; his reward is the dubious prize of now being the clear favourite to succeed – the one, in other words, with everything to lose.

It may seem like going back over old ground, but it is possible that if one of them had put himself forward, that would have been the alchemy required to produce the 45 signatures. One MP who was involved in compiling lists this time last year told me: "We were very close to having 45 names. What we didn't have was a candidate."

I mention this not-very-ancient history for two reasons. One is that it points to the importance of leadership – in the sense of taking the risk of putting oneself forward without knowing what might happen. The other is that the failure to have a contested election was a terrible mistake, for Brown and the party. Brown might have won, although funny things happen in leadership elections, but it would have been beneficial for the party to have had a campaign fought in a comradely spirit.

Those lessons ought to guide Labour MPs as they survey the post-Crewe prospect. Having spoken to several of them, I think that what has changed this weekend is that it has become the settled view of the parliamentary party that they are likely to lose the next election badly under Brown. This is partly a problem with Labour, but a large part is a problem with Brown. As one MP said to me: "We are approaching the point where almost anyone would be better than the incumbent."

Once that perception takes hold, it doesn't matter that nearly all of them nominated Brown a mere 12 months ago. If another change of leader might make the difference between a Cameron majority and a hung parliament, MPs will be driven by self-interest.

Therefore, I conclude that Brown is likely to be replaced as Prime Minister before the next election. One MP tells me that it could be before the summer recess, a mere eight weeks away: "We can't go on like this." But it is more likely to happen later this year or some time next year. It takes time for the cost-benefit analysis to soak through as far as the median member of the Parliamentary Labour Party.

Who will it be? David Miliband, Alan Johnson or James Purnell, probably. All three have charm and communicate well on television, although all have negatives. Miliband is untested by adversity, can come across as an arrogant intellectual, and is seriously green (I'm all for it, but people seem to take high carbon-fuel prices badly). Johnson said "I don't think I've got the capabilities" for the top job and ran a poor campaign for the deputy leadership. Purnell lacks experience and has a featherlight biography (Blair bag carrier and BBC bureaucrat). Less likely, but with some capacity to surprise, are John Hutton, Yvette Cooper, Andy Burnham or John Denham. Jack Straw might see himself as a caretaker leader, but that is hardly a leadership manifesto.

The mechanism is secondary. The complexity of Labour Party rules is beside the point, which is that no leader can survive the loss of confidence of his or her MPs. The most likely course would be Cabinet pressure to resign gracefully rather than face the humiliation of an open confrontation with Labour MPs. If private advice from allies were ignored, it might take a threat from a Cabinet minister to resign and say that Brown is the wrong person to lead the party into the election.

If that does not happen soon, we could see the tactic used against Blair by supporters of Brown being turned against him: that of the round robin. Indeed, Labour MPs could do worse than simply copy the letter signed by 15 of their number in September 2006, the letter that forced Blair to hand in his one-year's notice: "Sadly, it is clear to us – as it is to almost the entire party and the entire country – that without an urgent change in the leadership of the party it becomes less likely that we will win [the] election... We believe that it is impossible for the party and the Government to renew itself without renewing its leadership as a matter of urgency. As utter Labour loyalists and implacable modernisers, we therefore have to ask you to stand aside."