John Rentoul: Gordon's expensive mistake

Brown will get no thanks for protecting us if he is also trying to protect MPs with their snouts in the trough

I did not notice Gordon Brown making the terrible mistake, although I was there and watched it all. I was more interested in the seating plan for the Conservatives' new front bench: David Cameron had William Hague, his "deputy in all but name" on one side, and George Osborne, the shadow Chancellor, on the other. Next to Osborne sat Kenneth Clarke, back where he belonged, "the shadow shadow Chancellor" as the Prime Minister ego-checked him. The People's Ken grinned broadly and kept up a running commentary to Chris Grayling, the new shadow Home Secretary, on his other side. It wasn't until after Grayling that a place was found for a woman, Cheryl Gillan, the shadow Welsh secretary. On Hague's other side sat Alan Duncan, shunted sideways in last week's reshuffle, but placed one away from the leader to show that he had not been cast into the outer darkness. As I contemplated these arrangements, more complicated in their gradations of status than any country-house dinner, Brown was ploughing on, his body language confident and his argument driving through Cameron's cavilling.

The Conservative leader asked about the cost of the first wave of bank recapitalisation. Brown swept him aside, pointing out that the Tories supported it at the time, and had offered no alternative to the new bailout. Cameron: "He's behind the curve." Brown: "He's out of his depth." It was the usual stuff, down to Cameron's punchline, or, rather, Punch and Judy line: "If you want to ask us questions, have an election." It must have been good when it was first used, probably by Harold Wilson.

I thought Brown prevailed on the substance, although my distinguished colleague Alan Watkins comes to the opposite view on page 45. I did not pay much attention to the questions from Conservative backbenchers about the plan to exempt MPs' expenses from freedom of information law. Except to notice the weakness of the Prime Minister's case in his answer to Douglas Carswell. Brown said that the Government's proposals were for "more transparency than is the case in most parliaments in the world". In other words, our proposals are for something less than full transparency.

It was bad enough that Brown defended a plan to keep MPs' expenses secret. What I didn't realise was that it was worse than that. "Recently, the support that we believed we had from the main opposition party was withdrawn," Brown told Carswell. I should have realised that, whenever politicians refer to private deals in the Chamber of the House of Commons, someone is going to get hurt.

On this occasion, it was Brown.

The details of what deals were struck or reneged on are murky. Certainly, some of the grander Tory backbenchers are strongly opposed to having to publish every receipt for expenses over £25 – a threshold that was recently lowered from £250. But how Harriet Harman, who as Leader of the House is responsible for such matters, could have gained the impression that Cameron would have supported a cover-up is a mystery.

There are only two possible explanations. Either Harman took nods and winks from Tory backbenchers to mean that Cameron would back her scheme to restrict disclosure. Or Cameron led her into a trap, allowing her to think he would support it, before pulling out. Either way, Harman was naive. If Cameron were engaged in black ops, that would hardly have been a saintly thing to do, but the real fault lies with Harman and Brown for being so keen to hide expenses that they made a mistake.

Cameron's public position on expenses has been commendably clear. Not out of sea-green incorruptible principle, perhaps, but since the Derek Conway disaster – the Tory MP exposed for employing his son in a sinecure – out of a sound understanding of the brutal necessity of politics.

It is a brutal necessity that Brown just does not get. He told Edward Garnier, the second Tory to ask about expenses: "Far from spending a great deal of time this week on the issues that he is talking about, I am spending my time dealing with the problems of the British economy, and that is what I will continue to do."

The Prime Minister did not seem to realise that the expenses issue is part of dealing with the economic crisis. He will gain no credit for trying to protect people from the effects of the recession if he is also trying to protect MPs with their snouts in the trough.

It was an extraordinary mistake. What is even more extraordinary is that he went on making it even after it became clear that the Conservatives would not support the cover-up. Instead of ditching the plan before Prime Minister's Questions and taking the credit for doing what nearly everyone would think was the right thing, he defended it and let his spokesman tell puzzled journalists as he left the Chamber that the plan was being ditched.

Of course, there are arguments against full disclosure. There are a lot of pieces of paper, and a lot of people have to be employed to shuffle them, at a cost of £2m to the public purse so far, according to Harman. It doesn't matter. The principle is simple: that MPs are accountable for the public money they spend. It doesn't matter how inconvenient it is for them, or how intrusive, or how it offends the sense of entitlement to which they have become accustomed.

They simply have to accept it. The world has changed, and they have to change with it, as Barack Obama put it. Cameron understood that after the Conway embarrassment: he forced his MPs to declare all the family members they employed.

It defies belief that Brown doesn't understand it. It is a simple issue that cuts right through to the public. For many voters it is an issue that divides the parties just as much as their response to the financial crisis, and with just as much capacity to shape perceptions. While the economy is still hard fought, on this one, Cameron is on the right side of the issue and Brown – defiantly and unnecessarily – on the wrong side.