When David Cameron first faced Jeremy Corbyn at PMQs he eschewed attacks on the Labour leader. Rather than ridiculing his opponent, he cast himself as the respectful father of the nation. But at this week's session, his patience ran out. From the start, accompanied by jeering Tory MPs, he brandished his contempt for Corbyn. "If he wants to know who's heading for a winter crisis, I would say it's the Labour Party," he declared in reponse to a question on the NHS. "His media adviser is a Stalinist, his policy adviser is a Trotskyist, his economics adviser is a communist. If he's trying to move the Labour Party to the left, I'd give him full Marx," he added.

Corbyn had begun by again asking about tax credit cuts. "I asked him the same question six times last week ... He's had a week to think about it," he quipped. Cameron replied that the government's response to its recent Lords defeat would come in the Autumn Statement in three weeks' time, and asked of Corbyn: "If we don't reform welfare, how are we going to fund the police service? How are we going to fund the health service? How are we going to pay for the defence forces we're talking about today?"

The Labour leader went on to put a question from a Gulf War veteran, noting that a private in the army would lose £2,000 next April. But Cameron had a ready response: "What I would say to the serving soldier is he is now dealing with a leader of the opposition who said he couldn't see any use for UK forces ... That serving soldier wouldn't have a job if he were in power!" From that point, the PM dialled up the abuse, while Corbyn, true to his word, avoided personal jibes.

That Cameron no longer hides his scorn for Corbyn will be seen by some as a sign of weakness. But it more likely reflects the PM's confidence: the Labour leader's poor personal ratings mean he believes he has little to fear from ridiculing him. But the issues that Corbyn raised today - tax credit cuts and the NHS (rising waiting lists and deficits) - are hazardous territory for the government. Worse may be to follow as the planned spending cuts are imposed. If so, Cameron would be wise not to appear more concerned with attacking Corbyn than with addressing policy failures. But for now, the PM believes he has little to fear. The problem for the Labour leader is how many on his benches agree.