In one of John Mortimer’s Rumpole stories, the judge lets the defendant off because Rumpole has mounted such an incompetent defence. Can it be that Ed Miliband is pursuing a similar strategy at PMQs? For one can’t help noticing he virtually never wins one of these contests.

Miliband often starts rather well. Today, after some bipartisan exchanges about terrorism, he quoted David Cameron’s enthusiastic support at the time of the last general election for television debates between the party leaders. This was embarrassing for the Prime Minister, who has obviously changed his tune, and is now just pretending to be keen on taking part in the debates.

Cameron’s first response was weak: he just wondered why Miliband is “so frightened” of debating against the Greens. Miliband appeared to be making by far the stronger charge: namely that Cameron is frightened of debating against anyone.

But as usual, Miliband had no idea how to follow up his initial success, while Cameron – who benefits from having the last word – well knew how to move on to more favourable ground and mount a brutal counter-attack:

“With just ten of these sessions to go, he wants to debate having a debate. He can’t talk about unemployment, because it’s coming down. He can’t talk about growth in the economy, because it’s going up. He can’t talk about his energy price freeze, because it’s turned into a total joke…Please if he’s got any more questions left, ask a serious one.”

Tory backbenchers followed this up by reciting, at frequent intervals, the falls in unemployment in their constituencies, and attributing these to good old Oltep. This column likes to think of Oltep as a brilliant Hungarian economist who in early life discovered just how catastrophic the Soviet approach to economics was, and has since placed his services at the disposal of the British Conservative Party. But in order to conceal the identity of this shy, self-effacing genius from the Opposition, he is invariably referred to by Tory MPs as “Our Long-Term Economic Plan”: a term which throws everyone off the scent, for the word “Plan” has a Soviet ring to it, and distracts attention from the remarkably flexible approach to deficit reduction actually followed by George Osborne.

But what if the voters, on seeing Miliband in action, reckon he is so incompetent that the Labour programme really must be better and fuller than he makes it sound? What if they come to see Miliband as the plucky underdog, who deserves the support of all fair-minded people precisely because he seems always to be at such a cruel disadvantage? Rumpole did not mean to make such a bodge of his case: he won it by accident. A similar victory could still be within Miliband’s grasp.