Polls show a leap in support for the Liberal Democrats after Thursday’s leaders debate. Alex Snowdon investigates whether the Liberal Democrats can provide a viable alternative.

In the Leaders’ Debate there were two points at which Lib Dem leader Nick Clegg distinguished himself from his rivals.

One was when he called for smaller class sizes; the other was when he questioned the wasteful spending on nuclear weapons.

With both these issues Clegg gave the impression his party has distinctive positions, which are more progressive than the dominant Lab-Tory consensus in Westminster.

These moments, which were unusual in 90 long minutes of numbing agreement and banality (though, of course, there was plenty of superficial bantering to give the impression there are real differences), will have contributed to the Lib Dems’ extraordinary leap in the opinion polls.

YouGov polled a sample of the electorate after the debate and, as Liberal Conspiracy reports, Clegg’s party has shot up by 8 points to 30%, putting it ahead of Labour.

I’m surprised at the scale of the increase – and of course it won’t be sustained until polling day – despite it being clear to anyone that Clegg had given the strongest performance and would benefit the most.

Courtesy of a couple of policies, he was able to successfully position himself just a little to the left of Brown. This, combined with polished presentation skills, has evidently been enough to make a major impact on the viewing public.

YouGov reports 59% saying Clegg has had the best second week of the campaign, with only 14% opting for Cameron and 8% for Brown. That is spectacular by any measure.

Labour is relying – if the party is to prevent a Tory majority – on a layer of voters getting behind it, however reluctantly, as protection against an aggressively right-wing Tory government. But Brown did absolutely nothing in the debate to help that cause, steering clear of anything that might buck the stultifying consensus we’ve become accustomed to.

Instead we saw Clegg, in an admittedly very modest way, offering some hope to those who want to avert a right-wing, slash-and-burn regime.

As election day approaches it’s likely some of those swayed by Clegg will gravitate to Labour, if only for tactical reasons or because these spikes never quite last. However, if Brown doesn’t clearly distinguish himself from Cameron there’s a danger Labour will get stuck, making a Tory victory more likely.

It will also be interesting to see if the Lib Dems can sustain the myth that it offers something different. The contradictions in the party’s plans were hinted at in the TV debate, with Clegg following his comments on Trident with a warning that public sector pensions are too generous.

What we need, in fact, is the scrapping of Trident in order to fund services, pay and pensions in the public sector, as indicated by this excellent 1-minute video from Greenpeace:

Say No to wasting £97bn on new nuclear weapons from Greenpeace UK on Vimeo.

Nick Clegg was clever and skilled on Thursday night, but the reality is less appealing than the illusion some voters may currently be tempted by. A Lib Dem vote is absolutely not a vote for protecting public services and the welfare state. Britain’s third party shares the same assumptions as the Big Two, with only minor differences of emphasis.

A Tory victory will embolden the bankers and the bosses – and demoralise trade unionists and all those with progressive values. But whatever happens in this election, the essential task is building extra-parliamentary campaigns and championing an authentic, principled alternative to this miserably narrow mainstream.