Today, for the first time in almost two decades, there is a realistic prospect that the Conservative party will win the next election. Much will be made of the ideological contrast between Conservative and Labour, even though sometimes I find it rather hard to detect. But I hope that there will also be a very strong philosophical distinction between the two parties. New Labour cannot be fully understood until it is grasped that it is Britain's first postmodern government. The movement that surged to power in 1997 was formed less by Marx and Methodism and more by Foucault, Derrida and Richard Rorty.

We have abandoned the idea that there is an independent reality, which is out there and subject to independent verification – and adopted instead a different kind of political epistemology. The purpose of public argument has moved right away from truths that can be proven to narratives that can be constructed. This is formally recognised by the ruling elite. Peter Mandelson, one of the inventors of the new politics, speaks of the need to "create the truth".

So, we have entered a postmodern public discourse populated by rival truth claims. The core insight is that appearance and reality have become identical. The surface counts for everything. Government, therefore, ceases to be about getting things done – it's about being seen to get things done.

Britain has never enjoyed such an apparently active central government as over the last ten years. There have never been so many initiatives, press releases, New Deals, action plans. They key thing to understand is that all of this activity carries on almost entirely independently of life as it is lived by ordinary people. Despite official statistics produced by state employees to prove that they work, this blizzard of activity is actually part of a parallel universe. Douglas Carswell and Daniel Hannan have noted this phenomenon of virtual government in their book The Plan and they summon up Tony Blair's toe-curling memo calling for "eye-catching initiatives" as evidence. "The memo contained one sentence which bears particular contemplation," the authors note: "We also need a far tougher rebuttal or, alternatively, action." As Carswell and Hannan observe: "Blair had grasped that, in the contemporary political climate, rebuttal is action."

And this phenomenon is not merely confined to initiatives, press releases, government announcements and similar epiphenomena. It has also captured the legislative process. The Times columnist Matthew Parris was the first observer to note the emergence of "declaratory" legislation. "New laws and proposed new laws," Parris accurately noted last year, "are being touted around as though they were a specialised branch of advertising, rather than rules to be interpreted, enforced and obeyed." These laws, he noted, "do not so much do the right thing, as say the right thing."

A very nice example is the vast amount of government effort devoted to Sir Fred Goodwin's pension. Huge attention, from the prime minister, inside the cabinet, and among Treasury civil servants, has been devoted to this subject and it has dominated the news agenda for days. Yet it has no bearing on the profound economic crisis. What is going on here is a classic exercise in manipulation. The core concern of government is not, as one would hope and expect, to get Britain out of a mess. It is to divert attention onto Sir Fred – and to get itself out of a mess.

If the Conservatives are to govern effectively over the next decade, they need to turn their back on a philosophical doctrine that first took root in French philosophical salons in the 1970s. Instead of constructing the truth, as New Labour has constantly sought to do, they can start to reclaim the truth, and look back to their own roots in the British empirical tradition.

For an incoming Conservative government, this means two things: one a matter of detail, and one an issue of deep principle. First of all, the Conservatives must dismantle the apparatus of postmodern government. Above all, that means restoring the administrative function of the British civil service and downgrading its dominant presentational function.

But it also means looking truth in the face – and the success of David Cameron as prime minister will depend upon whether he has the courage and rigour to do this. As Margaret Thatcher said, on the occasion of the first Sir Keith Joseph Memorial Lecture:

"In politics, integrity really lies in the conviction that it's only on the basis of truth that power should be won – or indeed can be worth winning."

What Margaret Thatcher was saying here is that it does not pay to secure power through clever positioning or strategic alliances. That was the tragedy of New Labour – it was not honest about what it would do in office, which is why it failed as a government. David Cameron, I would guess, must be very straightforward with the British people. And that means putting out a much bleaker and tougher message of what he will do in power than he has tried to do so far.

This is an edited excerpt, by kind permission of the author and the Centre for Policy Studies, of Peter Oborne's Sir Keith Joseph Memorial Lecture, given on March 4 2009. The full text can be viewed or purchased here.