So it will have to be Blair, and not Brown, who rides to the rescue

The story of the past week in the long election campaign is simply told. Gordon Brown rode over the hill and failed to rescue Labour's faltering campaign. I am told that the Chancellor saw the dangers of being written up before the Budget as the sulking Achilles emerging from his tent to save the day, and was gloomy when a superficial reading of the newspapers suggested he might be cheerful. But there was nothing he could do about it, so he smiled dutifully for the cameras.

The story of the past week in the long election campaign is simply told. Gordon Brown rode over the hill and failed to rescue Labour's faltering campaign. I am told that the Chancellor saw the dangers of being written up before the Budget as the sulking Achilles emerging from his tent to save the day, and was gloomy when a superficial reading of the newspapers suggested he might be cheerful. But there was nothing he could do about it, so he smiled dutifully for the cameras.

And he delivered a clever and popular Budget. The £200 subsidy to pensioners was enough to sterilise an issue that threatened to turn septic. But it was never likely to be decisive in turning the political momentum in Labour's favour. Partly, this is because the public finances are tight, and there turned out to be less scope than I thought there might be for a pre-election giveaway. But partly it is because a tax cut would have contradicted the party's overall message, which Tony Blair and Gordon Brown unveiled jointly the next day.

The problem is that the message that the Budget was supposed to drive home was: "The Tories will cut £35bn from public services." That, in classic Brown style, is the dividing line. The choice at the election is between Labour public spending and Tory cuts. Now, I know that the Chancellor is still to some extent a semi-detached member of the Labour election team, but it is precisely the message that he would have devised had he been in charge, and he was publicly associated with it on Thursday. He stood benignly in the background while the Prime Minister engaged in a Socratic dialogue with Nick Robinson, the political editor of ITV News, about the meaning of the word "cut".

The curiosity is that Blair was defending a Brownite strategy. Back in October, one of the Chancellor's Blairite critics said: "At the next election you can't turn round and say the issue is investment vs cuts." If Labour's message is just "we're going to spend more money again", this critic said, the voters are going to respond: "Hang on, we've had about enough of that. We've had eight years of that." Who was that? It was none other than the Prime Minister himself, speaking to a private meeting of the parliamentary Labour Party.

Yet here he was, five months later, saying precisely what he had said the party couldn't say. And proving that he had been right five months ago. The actual numbers hardly matter: the sums are so huge that no one can have a sensible concept of how much £35bn is. The Chancellor's helpful ready reckoner, that it is equivalent to the amount saved by sacking every teacher, nurse and doctor in the country, hardly clarifies things.

Anyone who follows the campaign closely, or who read this column last week, knew that the £35bn figure is the difference between Labour and Tory plans for annual public spending in seven years' time. Now that Robinson has performed his public service by explaining it to a reluctant Prime Minister, more people understand that the "cut" is the notional eventual difference between planned spending increases under Labour and slightly slower spending increases under the Tories.

If the voters have to choose between public spending rising fast or a bit slower, the danger for Labour is that they might go for a bit slower. It is a danger to which the Prime Minister is particularly alert. Unnoticed in his supposedly "furious" but actually rather mild confrontation with "real" voters on Five television last month was this answer to a complaint about rising taxes: "Health and education were seriously underfunded, so we needed to get more money into those. But once we get to 2008, for example in the health service, we will then have hit the European Union average for healthcare spending, so you don't need to go on with exactly the same rises as have been now trying to build up."

Blair has been worrying for at least a year that voter tolerance of higher taxes has been "bumping up against the limit". His case is that New Labour has to move to a new phase in which, having secured a huge increase in public spending, reform of the way services are organised will start to deliver improvements without higher taxes. The Brownite argument, on the other hand, is that, having won round one, the party needs to go on to make the case for higher taxes still.

So far, the argument can be contained in a single Labour campaign. The "£35bn cut" message is, we are told, the first stage. It is designed to point out the difference between the Labour "enabling state" and the Tory "minimal state", by making the point that, over time, different choices of small degree add up to a yawning gulf. True, but the Conservatives have done enough to block the attack by promising to spend as much as Labour on schools and hospitals and more on pensions and police.

It was interesting, too, that Oliver Letwin, the shadow Chancellor, addressed his Budget broadcast exclusively to "Mr Blair". Never mind that one of the instances of Labour profligacy that he would cut was pot plants in the Department of Trade and Industry, he knows who the enemy is in this election.

Election campaigns in this country are presidential in style: this is a contest between Blair, Howard and Kennedy. Brown was never in a position to "save" Labour's campaign. Labour will regain the initiative only when it fights a Blairite campaign of spending on plus reform of the public services. The political strategists already huddled in the Labour war room in Victoria Street should write it on the "key message whiteboards" that overlook their desks: "Spending plus reform." The attack, rebuttal and broadcasting monitoring units should put Post-It notes on their television screens: "Don't forget the reform."

It is a campaign that can be fought only by Blair because Brown has demonstrated by his hostility to health service reform and to higher university tuition fees that he does not really believe in it. Or that he is too gentle towards the prejudices of the Labour tribe that will choose the next party leader.

The story of the next six and a half weeks of the election campaign is therefore also simply told. It is not Gordon Brown who will ride to the rescue of the Labour cause; it is the Prime Minister. It does not really matter that everybody hates him, or that people are generally better disposed in a mild sort of way towards the Chancellor. When it comes to getting the message right, it has to be Blair. Besides, for all the wear and tear on his reputation, Blair remains the supreme communicator of our age. He will have to save the day.