Now is the time for one good man to come to the aid of his party. David Miliband, your country needs you. Gordon Brown's chances of winning the next election are negligible and getting smaller. I keep reading that it is "too early" to write him off. On the contrary, it is too late to do anything else. He had his chance. It did not last very long, but he had a honeymoon. He used it to put a new-minted reputation for plain speaking and sober leadership through the shredder.

After Christmas he had time to regroup, hire a new team and take stock. And any honest stocktaking must conclude now that it is, in effect, all over. His opinion poll ratings stopped getting worse for a while, but now the Conservatives have settled on an average nine-point lead. That is what is known in the City as a dead cat bounce.

Surprisingly, though, those who are most eager to tell me that it is "too early" to write off Brown include members of the shadow cabinet. One said last week that he was worried Ken Livingstone "could squeak it" next month, and that his re-election as London mayor would lift the Prime Minister. But it would make little difference. The election of Boris Johnson would be a setback for Labour, but the converse doesn't hold. Brown is so distanced from Livingstone that he would gain little by his unexpected victory, while the continuation of the status quo can hardly harm the Tories.

The status quo is that of a drift away from Brown that is almost impossible to reverse. One pollster, Populus, reminded its respondents last week, "It is now just over nine months since Gordon Brown has been Prime Minister." It then asked how he compared with Tony Blair. Only 14 per cent thought he was better, 31 per cent worse and 53 per cent the same.

One year ago, Miliband, who was then Environment Secretary, was hooted by the BBC Question Time audience. He said: "I predict that, when I come back on this programme in six months' time or a year, people will be saying, 'Wouldn't it be great to have that Blair back because we can't stand that Gordon Brown?'" And so it came to pass.

He has not actually been back on the programme since then, but my point is that he should be. Now is the time for him to start to set out his stall for the future, because Brown's premiership will implode amazingly quickly. These things do.

Look at what happened in 1990. Margaret Thatcher seemed unassailable. She had seen off a "stalking-horse" challenge to her leadership from Sir Anthony Meyer the year before, and had spun the media to present the local elections as a success. But Tory MPs were worried about their seats, and six months later she was gone.

Today, there are similar whispers among Labour MPs. One told me he was "absolutely spitting" at the disloyalty shown by the plotters who pushed Blair out to save their seats and who now say Brown is worse. As we report today, Labour MPs are talking of a stalking horse – the difference being that Charles Clarke needs 70 of his colleagues to nominate him; Sir Anthony needed two. Now, as then, the rules for leadership elections are being debated. Already, a motion calling for a cut in the number of MPs needed to nominate a candidate is on the agenda for the Labour conference in September. Now, as then, the government whips are telling MPs not to take part in media surveys.

That is because surveys and opinion polls become part of an accelerating cycle that will drive the Government into meltdown. I agree with my colleague Alan Watkins, Lord Watkins of Longer View, writing on page 57, that Brown's problems are terminal. But I take issue with him when he suggests that Brown will not be replaced before the election.

It is true that, as one studied the form guide helpfully published by The Sun last week, none of the nine candidates stands out as a credible alternative prime minister in the way that Michael Heseltine once did. Ed Balls, David Miliband and John Hutton were the first three listed, and the only three worthy of consideration at this stage. Certainly Balls, Secretary of State for Children, has the brains and the drive. Jack Straw is not the only Cabinet colleague who has been aggrieved by his territorial ambitions over patches of Whitehall turf. John Denham, who took over the part of the old education department in charge of universities, has had to repel repeated incursions into the demilitarised zone that divides the old barony.

It seems unlikely, though, that Balls will have the numbers behind him when the opinion polls become crucial in deciding the outcome of Labour's leadership crisis.

His Conservative shadow, Michael Gove, accuses him for subordinating education policy to his leadership ambitions. If only. If Balls were serious about going for the leadership, he would be trying to convince parents that he is ferocious for their interests. Instead, he seems to have decided that his strategic objective is to reassure teachers and local councils. Although he is right in principle in his dispute with church and Jewish schools, it looks too much like an attempt to pick a fight with good schools.

That might make sense if the leadership were decided by Labour Party members, who include a disproportionate number of teachers and local government officials. But that is an illusion. Yes, Labour members have one-third of the votes, but a contested election will be decided largely by opinion polls telling the party who is most likely to lead it to election victory.

And that won't be Balls. Nor, sadly, will it be Hutton, who is as aggressively New Labour as Balls isn't. Neither seems to have the potential to connect with a mass electorate in a way that offers a significant premium to Brown.

So David Miliband: this is it. You have the qualities that could put Labour back in contention. You have the poise, the communication skills and just enough experience at the highest level. But you require courage and a campaign of self-promotion to a general public that still has only the haziest idea who the Foreign Secretary is.

A senior member of the shadow cabinet surprised me recently by saying candidly that he thought Miliband was Labour's best option. He thought the Foreign Secretary comes across as "weird", which is plainly how the counter-attack would be framed, but it was clearly a subject to which the Tory high command had already devoted considerable thought.

Another friend of David Cameron told me that he thought Cameron would "run rings" round Miliband, but I do not agree. The Foreign Secretary would meet the Tory leader head on where he is strongest: youth, freshness and energy. When it comes to policy, Miliband can outflank him on the environment and knows his way around public service delivery.

He has started to push off from the quay. Last month he went head-to-head against his shadow, William Hague, on the Today programme: not many Cabinet ministers have the confidence to do that. Before last weekend's Progressive Governance summit, he wrote an article for The Times that hinted at radical innovation by "chains of schools and health services". He said: "A world-class head teacher should not be confined to managing one school." A takeover in the private sector "injects new ideas, people and capital. We need its equivalent in public services."

We need more of this, much more. And we need it now. The Brown meltdown could happen at any moment.