Leading article: A glimpse of the new political battleground

The surreptitious way that the Chancellor of the Exchequer slipped out the bad news in his pre-budget report yesterday - namely that UK economic growth this year will be half of what he predicted - was almost comic. It takes some chutzpah to casually mention before the House of Commons that what you predicted to the British people one month before a general election was very wide of the mark.

But Gordon Brown is entitled to a little chutzpah. His record remains formidable. The Chancellor's stewardship of the economy has delivered 34 consecutive quarters of growth. And in spite of all that is happening in the world, Britain has reasonable growth, controlled inflation and low unemployment.

In the light of this, the Shadow Chancellor's fierce attack on Mr Brown was over the top. Nevertheless, the shine is beginning to come off the Iron Chancellor's record. As Treasury growth predictions are downgraded, and public borrowing increases, the credibility of the Chancellor's "golden rule" is diminishing.

Mr Brown's fundamental problem is revenue. The Chancellor has consistently overestimated the Government's tax take in recent years. This black hole in the public finances is proving ever harder to conceal. A shortfall will eventually mean the need to either cut spending or raise taxes - both very damaging politically. A series of windfall taxes and promises to improve public sector efficiency have kept up appearances so far. But this cannot go on: unless growth picks up next year, Mr Brown will find himself in serious difficulties.

But, in truth, most of this was obvious before yesterday's speech. More interesting was the preview provided of the emerging political landscape. Mr Brown, the Prime Minister-in-waiting, gave a speech designed to shore up both his record and his right to the top job. He rubbished the Tory idea of redistributing the proceeds of growth between tax cuts and public spending - a shrewd move, since this is likely to continue to be a source of acute division in the Tory party. And by championing a housing scheme to help public sector workers into the housing market, he made a pitch for the support of the aspirational middle classes. This was politics at its most naked. Expect much more of this as the Chancellor prepares for the switch to Number 10.

On the other side, we saw the first indications of how a youthful new Tory team will confront their experienced opponent. By repeatedly labelling the Chancellor a "roadblock to reform", they hope to exacerbate tensions between Mr Brown and the Prime Minister and underline their claim to inherit Mr Blair's crown. It is an accusation that has the potential to wound since, as Mr Blair has indicated, his reforms have been held back by his colleague; pensions reform is merely the latest manifestation in a long, protracted struggle.

Mr Osborne, however, failed to draw much blood yesterday. The Tories will struggle unless they ditch their own obsession with tax cuts; instead, they should concentrate on demanding improved public sector efficiency. They might have also questioned yesterday the manner in which the Chancellor took it upon himself to distribute the assets of unclaimed bank accounts. There is nothing wrong with the causes that will benefit, but it is a statist manoeuvre resonant of Old Labour.

What was really on display was a sign of the emerging order in British politics. Mr Brown, for so long impervious to criticism, demonstrated once again his political brilliance. But there were signs of fallibility. The Tories, still struggling with their inheritance, showed that they might be ready to exploit the emerging cracks. Yesterday, we were given a glimpse of the new Westminster battlegrounds.