SO now we know why David Cameron chickened out of head-to-head debates with Ed Miliband, after he came off second best in tonight’s TV showdown.

The first bout of the TV campaign showed us a prime minister surprisingly discomforted and nervous, at first – and a Labour leader confident the wind is in his sails.

First up was Mr Cameron, with a seriously shaky start when confronted with the famous death stare of Jeremy Paxman, attacking hard on rich mates in the Chipping Norton set.

Clearly prepped to repeat the favourite Tory catchlines – “the economy is growing, people are back to work” – Mr Cameron found himself grilled about the surge in foodbanks, zero-hours contracts and tax avoidance.

And Paxo really hit home when – three times – he demanded to know where £12bn of Tory welfare cuts will come from, with no answer forthcoming.

“Do you know and you are not telling us - or do you not know?” he sneered. It was a good job Mr Cameron had piled on the powder, or the sweat would surely have flowed?

Later, Mr Miliband floundered when he said spending was “likely to fall” – “that’s a bit of a weasel word” – and on the criticisms that he’s a “North London geek”.

The Northern Echo:

But he pulled off the high-risk strategy of taking on the fearsome Paxo - “You asked me a question – let me answer it”, “You’re important Jeremy – but not that important!”, the second to audience laughter.

And he nailed the toughness question, pointing to his stance on facing up to Obama on bombing Syria. “Am I tough enough – hell yes, I’m tough enough.”

Partly, Mr Miliband’s superior performance reflected weaker questions from Mr Paxman – who peaked early with some supercharged sneering at the prime minister.

But what the captivating exchanges showed is that it is far easier to be the challenger with less baggage, than to be the incumbent with a tricky record to defend.

That’s why Mr Cameron won’t go near a head-to-head debate – and why last night will not have changed his mind, unfortunately.