When all else fails, Ed Miliband resorts to class war. The Labour leader’s best line today (in a weak field, it should be said) was: “If you’ve got big money you’ve got a friend in this Prime Minister, if you haven’t he couldn’t care less.”

Miliband feels comfortable saying this kind of thing. He knows he is touching his opponent on a sensitive spot: the Conservatives suffer from being seen as a party of the rich, who don’t care about anyone else, and David Cameron has never developed an entirely satisfactory response to such gibes.

But the main reason why Miliband feels comfortable saying such things is that he is able to indulge for a moment in the pleasant illusion that he is on the side of the poor. Politics, he can pretend, consists of a class struggle in which victory will go to the proletariat, ably commanded by Comrade Miliband. It is a delightful fantasy, in which Miliband, waving a red flag and sporting for the occasion a worker’s cap, leads the revolution which shatters the black forces of capitalist reaction commanded by Cameron, who in order to make it perfectly clear that he is on the side of the bosses, consents to wear a top hat.

Karl Marx, who became the most influential North London intellectual there has ever been, wrote a number of penetrating works, including The Eighteenth Brumaire of Louis Napoleon, in which he argued with persuasive brilliance that class struggle has played the dominant role in history. But if Marx were alive today, it is generally agreed that he would be intelligent enough to see that various aspects of his theory require modification. And there is in fact a rather good book, Parliamentary Socialism by Ralph Miliband, which demonstrates, as the author put it in a Postscript published in 1972, that “the Labour Party remains, in practice, what it has always been – a party of modest social reform in a capitalist system within whose confines it is ever more firmly and irrevocably rooted. That system badly needs such a party, since it plays a major role in the management of discontent…”

Ralph Miliband’s younger son, who now leads the Labour Party, finds himself reduced to a mere prop of the capitalist system, his function being to enable malcontents to vent their anger by constitutional rather than revolutionary means. But Miliband the younger is not actually much good even at playing that subsidiary role, which appears to have been seized from him, at least for the time being, by UKIP. No wonder he looks, despite a brave pretence of relish for the fight, a bit down in the mouth.

There was of course no time, and no desire, to go into all this at PMQs. Miliband, Cameron and their rival parties of hooligans exchanged a few insults and went off to lunch.