PMQs verdict: Harman struggles, but pins Cameron down on tax credits

It was nothing flashy, but Harriet Harman came out of PMQs having achieved much more than it first appeared.

The acting Labour leader is waiting – seemingly forever – for someone to take over. She can barely hide the fact she doesn't want to be there anymore. Harman is a very capable public speaker and politician, but she's just not into it at the moment. She radiates exasperation, like a teenager in the back of a car on a long journey. Cameron always seems to like and admire her, so it's all fairly respectful, if a little dull.

He dealt with her pretty well and will be perfectly satisfied with his performance. There were certainly no knock-out blows. But Harman did pin him down on tax credits, a benefit paid to people in work but on low wages. Her party – which still seems in shock, incidentally – should be grateful to her for it. There's potential here to carve out a political space on benefits which satisfies Labour's soul and the public mood.

Cameron's speech on benefits and income this week focused on the use of tax credits as a form of subsidy for low wages. He rightly said this couldn't go on. This has long been a call of the left, which envisages forcing corporations to raise wages instead of making the taxpayer shell out for it. Cameron has emulated that call, except without the second bit where wages rise. So it's basically an impoverishment agenda sold in a One Nation ticket.

The Tory leader said he intended to get "more people into work, get them better paid and cut their taxes". Harman pointed out that a cut to tax credits would cost the average family receiving them £1,400 a year. She followed this up with a pretty stale PMQs-style dig – "I know he doesn't have to budget but many families do" – which temporarily sent the Commons into an uproar. But she was far more effective when she was being structured and forensic in her questioning. For a single mum, she said, the minimum wage would need to go up by 25% overnight to make up for what Cameron was taking away.

Cameron's reply:

"The problem with what the honourable lady says is that the last government didn't budget for the country."

Again, the Commons went into uproar, this time because it was Cameron himself who was in charge of the last government. This slip-up is actually quite revealing. It shows how old the line is and how unhelpful it is starting to become. The time is coming when he will no longer be able to rely on his it's-all-Labour's-mess-and-we're-just-cleaning-it-up angle. It was tired a couple of years ago. A couple of years from now it'll be insufferable.

But the important part of the exchange wasn't about what he said, but what he didn't say. At no point did Cameron deny the fact he was going to cut tax credits. There was also a noticeable omission from his response to the wage increases families would need to make up for that lost cash.

The prime minister said:

"We're seeing rates of pay go up because we've got a strong economy."

In other words: there will be no corresponding drive to increase the minimum wage once he cuts tax credits. Cameron had given the game away. He would cut tax credits and do nothing to boost minimum age. He then added, rather shamelessly:

"If you don't get people back to work and reduce welfare you're going to have to make deep cuts to the NHS."

The NHS is at this point just an emotional trigger, the threat to it acting as the justification for every cut the Tories want to make. But the real nonsense behind the statement was that this had nothing to do with out-of-work benefits. His only response to the questioning was to address something else entirely.

Harman got irritated with Cameron's attempt to drag a debate on the sort of hard-working low-income families Cameron ostensibly wants to help into the tabloid terrain of workshy scroungers. But actually, it was a revealing comment. It showed Cameron is not confident with the argument. He feels he's on dangerous ground. And that's because he is. If you, as a government, spend years telling people to go to work, it's best not to cut the income they can get once they do what you suggested. One might even suggest that cutting tax credit is a disincentive to work.

For all her exasperation, Harman got some valuable information out of the prime minister today. He's going to cut tax credits, he has no policy with which to replace the income from employers and he is nervous about the debate. It wasn't bad work for someone who seemingly didn't want to be there.