Conservative commentators have long argued [2] that one of the reasons the Tories failed to win a majority at the last election was the inclusion of Nick Clegg, the "none of the above" candidate, in the TV debates. The Lib Dem surge forced the party to direct resources away from attacking Labour and helped deny them victory in key marginal constituencies (the Conservatives finished second in 38 of the 57 seats won by the Lib Dems). A ConservativeHome survey [3] of 109 Tory candidates in 2010 found that 91 per cent agreed that "the election debates gave the Liberal Democrats by-election status, and disrupted an already disjointed Tory campaign".

In view of this, it's unsurprising that David Cameron is determined not to repeat this tactical error in the case of UKIP. If and when the TV debates happen (and it remains a big 'if'), Nigel Farage's party, which stands a chance of winning the European elections in 2014, will undoubtedly push for inclusion. A recent ComRes poll [4] found that 54 per cent of people believe Farage (who put in a typically assured performance on last night's Question Time) "should be offered the opportunity to take part alongside the other main party leaders". But in an interview with the House magazine [4], Cameron makes it clear that he's not one of them. He tells Paul Waugh and Sam Macrory: "Obviously, we have to decide on this nearer the time, but the TV debates should be about, you know, the parties that are going to form the government, in my view."

As you might expect, Farage has responded by describing Cameron as "embarrassingly out of touch". He said: "If UKIP's share of the opinion polls were to continue as they are now, to exclude us from the debates when the Lib Dems were included last time would make British politics look as outdated as the closed shop and embarrassingly out of touch.

"If he wants to restrict it to those parties who are likely to form the next government, he'd better not be booking studio time himself with confidence."

But Cameron makes a reasonable point. Though casually described as the UK's "third largest party [5]" after outpolling the Lib Dems in recent months, UKIP still have no MPs and will be lucky to improve on this performance at the next election. Yet it is still likely to prove harder to justify the exclusion of Farage than it was to justify the absence [6] of Alex Salmond in 2010. In the case of the SNP, the three main  parties can at least argue that only those parties competing to form the next Westminster government should be included, but this argument doesn't apply to UKIP. If the party is polling at least five per cent in 2015 (the threshold normally required for representation under a proportional system) then the right-wing press will likely demand the inclusion of Farage.

Incidentally, one guest at Wednesday night's ConservativeHome new year reception told me that George Osborne (that night's guest speaker), who remains the Conservatives' chief election strategist, has, in effect, declared that the debates will take place "over my dead body". So, as I said, don't count on a repeat in 2015.