But does this principle apply to democratic politics? Can a losing party reverse its fortunes simply by adopting the policies and slogans of the party that keeps beating them to power?

The Tories certainly seem to think so and the chattering classes mostly agree. Evidence the enthusiastic response last week to David Cameron’s embrace of new Labour policies on health, education and taxes, and on Tuesday to his self-conscious echoing of Tony Blair’s very first slogan, when the Tory leader promised not only to deal with Mr Blair’s “respect agenda” but also to focus on “the causes of disrespect”. A consensus is desirable if it is on policies that genuinely make sense. But what will it do to the country’s political culture if all its leaders chase each other’s tails like three dogs running in circles around a lamp-post planted on the “centre ground”?

One answer comes from across the Channel, where politics is paralysed in all three of the great nations of Europe — Germany, France and Italy — by the refusal of politicians to debate serious issues such as the future of the European Union or the welfare state. Another, very different, but even equally disturbing message comes from America, where the success of George W. Bush’s “compassionate conservatism” is seen as an explicit model by the Cameron campaign.

Which of these examples turns out to be more relevant for Britain depends on whether the consensual politics of the Tories under Mr Cameron represents a genuine ideological conversion or merely an electoral trick.

Suppose first that the Tories are genuine in their sudden enthusiasm for high taxes, rising public spending, anti-elitist education and a totally government-financed health service. Britain then faces European-style paralysis in the years ahead. Not only can we rule out any radical change in the structure or the quality of the public sector, we can also rule out even the possibility of a serious debate on the role or the size of the State.

Just as European voters today are offered no real choice by their parties on issues such as EU integration, economic liberalism and the burden of taxes, the only choice for Britain will be big or bigger government, high or higher taxes and public service bureaucracies managed by Tweedle-Dum or Tweedle-Dee. The three most important growth industries of the 21st-century economy — health, education and pensions — will continue to be monopolised by the public sector. In short, the commanding heights of the economy will be dominated by the Government to an extent that Herbert Morrison could only have dreamt of in 1945.

The long-term results are likely to be the same as they were in the 1950s and 1960s: the British economy will move back into long-term decline, not only because government spending and taxes will rise relentlessly as a share of national income, but even more because what should be the most dynamic industries powering Britain’s future will be run by the State. And whatever the born-again social democrats surrounding Mr Cameron may say about the alleged efficiency of a tax-financed NHS in comparison with the insurance-based models employed in other countries, experience suggests that competition among profit-motivated producers for the custom of price-sensitive consumers always beats the “efficiency” of central planning over time.

The Tory conversion to European-style Christian Democracy, if genuine, would transform politics even if Mr Cameron never won power. The Tory abandonment of Thatcherism would change the Labour Party’s internal dynamics, shifting its centre of gravity to the Left. The result would be a new consensus, demanding ever-higher government spending and negating pressures for privatisation and public service reform.

But what if the Tory conversion to social democracy is just a tactical device? If this is the case, we should look to America for clues on how British politics might evolve. Mr Bush won the presidency by pretending to be a centrist “compassionate conservative” and pushing Al Gore to the unelectable Left — just what Mr Cameron hopes to do to Gordon Brown.

Once Mr Bush won, he quickly changed his colours and emerged as the most right-wing, ideological President in modern American history. In the same way, many Tory politicians predict that Mr Cameron, the author of the last election manifesto, would re-emerge as a Thatcherite true believer the moment he won the keys to Downing Street.

In this scenario, Mr Cameron’s centrist rhetoric would turn out to be just spin, designed to get the Tories back into office. Once elected, the Tories could revert to their true agenda of tax cuts, privatisation and public service reform. This cynical strategy, which worked like a dream for President Bush, is what keeps hope alive among the many Cameron supporters who still admit (at least in private) to Thatcherite leanings.

But within months of his election, Mr Bush’s popularity slumped to unprecedented lows. Had it not been for 9/11, Mr Bush would almost certainly have lost the 2004 election. Moreover, Mr Bush’s effect on American politics has been far from welcome to the “Thatcherite component” of the Republican Right. He has increased public spending faster than any president since Lyndon Johnson and been the first President never to veto a spending bill.

By falsely presenting himself as a consensual centrist, Mr Bush was never able to win an honest mandate. He became a hostage to special interests from the moment he was elected and, in the absence of 9/11, he would have remained a lame duck. “In office but not in power” over a drifting directionless Administration. Is that the best that Britain can expect from the post-Blair consensus?

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