Leading article: Mr Blair must beware... the centre of British politics is not his by right

It seems almost incredible that only eight months ago Labour was celebrating its third straight election victory. The Tories had been vanquished again. The Government had been returned with a majority that would have made many previous prime ministers positively green with envy. And Tony Blair was reconfirmed as master of the British political scene. How quickly things have changed.

The past few weeks have been particularly torrid for the Prime Minister. Gone is the image of a confident statesman, in control of events, and securing his triumphant political legacy. In its place is a beleaguered leader stumbling around, putting out one fire after another. The gathering resistance of the police to force mergers is merely the latest indication that Mr Blair's authority is on the wane.

This shift is partly a result of the fact that the country finally has an opposition party worthy of the name. Opinion polls this week showed that the Tories, under the leadership of David Cameron, are ahead. For the first time since 1992 - with the exception of a brief period during the 2000 fuel crisis - the Conservative Party has overtaken Labour. And it has done this by moving sharply back to the centre ground and demonstrating signs of a credible strategy. Rubbing salt in the wound yesterday was Oliver Letwin, who hinted that one of the new Tory objectives will be to "redistribute" wealth. This is the sort of expectation-confounding coup that New Labour might have engineered in the early days of Mr Blair's leadership.

The Prime Minister's tormentors are not confined to the opposition benches. Labour MPs have threatened to defeat the forthcoming Education Bill unless it is substantially modified. There is also looming internal strife on a range of issues from health to nuclear power. Mr Blair ought to take this seriously. Having inflicted the first Commons defeat of the Government over 90-day detention last month, his backbenchers have tasted blood.

Mr Blair will need to exercise all his powers of persuasion if he is to see the bulk of his "legacy" legislation enacted. Threats to quit unless he gets his education and health reforms through sounds bold, but he should beware. This is a weapon that can be used only once. Perhaps more appropriate would be a statement of clarification from Mr Blair about when exactly he intends to stand down. The Prime Minister's pledge "not to fight the next election" increasingly looks like a misjudgement. It has generated uncertainty about how long the Blair era will last. It could be months; it could be years. But it is not surprising he is having difficulty exerting his authority.

One can have a degree of sympathy for Mr Blair. His deputy's outburst at the prospect of poor schools "improving" shows the strength of the forces of conservatism within his own party. This roar from an old Labour dinosaur shows why reform is so necessary in education and why Mr Blair is right to push for it.

John Prescott's silly rant serves another purpose too. It offers a timely reminder of Mr Blair's achievement in making the Labour Party electable. It was because Mr Blair marginalised such anachronistic figures that Labour won power. The big question in British politics now is whether Gordon Brown can keep his party content while pressing forward with lesser reforms, or will this merely allow Mr Cameron to emerge as the candidate offering to continue the modernisation of British public services.

There is movement at the heart of the British political scene and in the electorate. People are less tribal. Allegiances are more fluid. This is why the Tories' move to the centre has the potential to change everything. Politics has rarely been more fascinating.