At PMQs today, Jeremy Corbyn had Theresa May on the run – Tory policy is now decided by the Labour Party

The Labour leader asked about universal credit for the third week in a row. Theresa May was better prepared than last week, but her answer was essentially, “Hardly anyone is on universal credit and most of those few are happy.”

Jeremy Corbyn, whose ring of election confidence still surrounds him like an invisible force field, took her statistics and flung them back at her. If only 8 per cent of claimants are on universal credit after seven years, and 20 per cent of them are dissatisfied with the service, is that not “cause for thought”, he asked mildly.

This is much harder than it looks, but it is the key to an effective performance in the House of Commons. You have to listen to what the other person is saying, work out what is wrong with it and respond to it in a way that makes this clear, especially to your own side. Before the election, Corbyn couldn’t do it at all. Now he keeps making the Prime Minister look uncomfortable by immediately rebutting her claims.

Even so, I couldn’t tell whether he even spotted the significance of May’s answer to the question before his. She told Kevin Forster, the Conservative MP for Torbay, that the housing benefit cap would no longer apply to the social housing sector. This is a huge climbdown, but because it was phrased in technical language about the LHA, the Local Housing Allowance, hardly anyone in the Chamber understood it.

But housing is the one specialist subject that Corbyn really does know about, and so he should have known what it meant. It is a big retreat from the benefit cuts pencilled in for the rest of this Parliament, and, in effect, another big spending commitment in next month’s Budget.

If Corbyn had been even better at politics, he would have said this was a humiliating U-turn, forced on a weak government by Labour pressure.

As it was, he was right to press ahead with the attack on universal credit. He knows and the Prime Minister knows that he has the Government on the run on what she calls “You See”. (She does like her abbreviations: LHA, UC and even a “previous PMQs”.)

Last week, Theresa May retreated by making the UC helpline free. And everyone knows that she will soon have to retreat on the initial six-week delay in making UC payments. If her only defence is that hardly anyone is on UC and it will take another five years to roll it out to everyone, that built-in hardship trap is going to have to go to make it possible. Too many Tory MPs are already restive about it. Another huge expense for Philip Hammond to stump up in the Budget.

Corbyn also built up to a good peroration in which he listed all the ways in which the Government didn’t know whether it was coming or going (“Going!” Labour MPs shouted happily). He was interrupted by the Speaker before he could bring it to a suitably pithy conclusion, which probably saved him from shouting on for too long.

The Prime Minister knows her defences have been breached. Her attacks on the last Labour government for bringing in working tax credit bounce off Corbyn, who spent all his time opposing that government (and besides, even fewer people understand Gordon Brown’s tax credits than understand UC or LHA). The only deep cheer she roused from the Tory benches was when she attacked Corbyn for “disrupting Brexit”. Which was ironic on a day when the Brexit Secretary himself had said there might be a “meaningful vote” on the Brexit deal after we have left the EU.

She knows that Government policy is decided by the Labour Party on any subject on which it can peel off 20 or so Tory rebels from her side. Universal credit, benefit cuts, the NHS, schools: the whole range of domestic policy. The Chancellor is going to have to find money from nowhere and he has just one month to find it.