Liberal Democrats surprise UK

There's a useful aphorism from across the Atlantic. The winners grin; the losers spin. So it has been since the first British televised leaders' debate gave an electric jolt to a hitherto low-wattage campaign. Peter Mandelson, Alastair Campbell and the rest of the Labour college of spin doctors and truth surgeons have tried to present the bout as a victory for their candidate on "substance". Translation: Gordon Brown made his characteristic, elemental error of thinking that the way to the nation's heart is the robotic recital of lists of statistics. The agreeable Alan Johnson suggested that it did not matter if the prime minister was a leaden performer because "this is not a popularity contest". Alan, allow me to let you into a little secret about a general election: a popularity contest is exactly what it is.

Over in Tory spin world, Team Cameron's propagandists have been shrugging about the viewing figures even though more than nine million was a highly respectable audience for 90 minutes of politics without an ad break. Tory spin-meisters point out that many voters didn't tune in and the winners of US presidential debates don't always win the actual election.

And the Lib Dems? They, of course, are the ones wearing the grins. And they are not just any old grins; these are ear-to-ear, cheek-aching grins with their leader's triumph. His pre-debate negotiators created a platform for victory by securing even airtime and status with his two rivals, the like of which has never been enjoyed by any previous leader of the third party.

Credit, though, where it is primarily due. Having got his chance, Nick Clegg did not blow it. He could have looked incidental and marginalised in the company of the other two. That is his weekly fate at prime minister's questions. His skill was to use the debate to make himself look the equal of Brown and David Cameron as well as a personable, reasonable and refreshing alternative to both of them. Many Tories are grinding their teeth and cursing their leader for gifting the Lib Dem this opportunity to shine.

Unfettered

There were deeper reasons for Clegg's victory, which tell a wider story about this election. Brown came into the studio clunking behind him the same ball and chain which he is forced to drag the entire length of the campaign trail. He is the unpopular leader of a government that has been in power for 13 years. Cameron also sagged under the weight of his baggage in his case, it is the number of changing and sometimes conflicting positions he has adopted over the past four years. Clegg possessed the great advantage of having a simple, clear message that fitted with his wider campaign. That message is that Britain has been let down for decades by the other two, the duopoly which he derides as the "Labservatives".

A "plague on both your houses" is hardly a novel line. This has been the tune of third-party leaders since the Beatles were an unknown Liverpudlian boy band. It is working so well for Clegg because the voters are now particularly receptive to that song. The parliamentary expenses scandal has intensified public alienation from establishment politics to the advantage of the leader who can present himself as an insurgent outsider.

Very senior Tories are now ruing their failure to develop a strategy for dealing with the Lib Dems before the campaign started. The Conservatives were complacent in assuming that they could simply squeeze the third party into irrelevance and cruise to victory on the slogan of change. They now have to deal with Clegg out-doing Cameron and presenting himself as the fresher and more sincere face of renewal.

Entering the middle stretch of the campaign, they are all presented with some unexpected dilemmas. The Lib Dems are keen to capitalise on this boost, but don't seem entirely sure how, and are wary of the hype for fear that it will set up Clegg to flop at the next debate, which he goes into with greatly raised expectations.

Some Labour strategists have sounded happy to join the praise for his performance in the first bout. That was before the YouGov poll which had the Lib Dems sucking support from both the other two, leapfrogging Labour and breathing down the necks of the Tories. Cameron's strategists are already arguing among themselves about how aggressively they should "take the fight" to Clegg.

The risk for the Tories is that Cameron could be lured back on to Michael Howard territory and this would look like a lurch to the right which is repulsive to the liberal, centrist voters that he needs. The trouble for both the Tories and Labour is that being "outside the mainstream" does not look the least bit "eccentric" to the many voters distrustful of and disillusioned with the old duopoly. It looks jolly attractive.

Andrew Rawnsley is the The Observer's award-winning chief political commentator as well as being a best-selling author and critically-acclaimed broadcaster.