Andrew Grice: Why public revulsion forced Brown to act

Why did Gordon Brown suddenly take the initiative on MPs' expenses? He has been shocked by the scale of public anger about the recent torrent of stories on MPs' claims. The current system, particularly the "second homes" allowance, is mistrusted. People think MPs are in it for themselves, bringing politics into disrepute.

Secondly, voters think politicians are not addressing the issues that matter to them – notably the recession. The economy is Mr Brown's preoccupation, and his best hope of avoiding defeat in next year's general election. But his message is often drowned out by noises off.

Thirdly, the Prime Minister knows the expenses controversy is going to get a whole lot worse in mid-July, when 700,000 pages of MPs' previous claims will be published. No surprise, then, that his new rules would take effect on 1 July if MPs approve them next week. Mr Brown would be able to claim that the Augean stables had already been swept clean – and to resume his Herculean labours on the economy.

The Brown "crackdown" on expenses is not an attempt to reassure the public that he is squeaky clean after the damage he suffered from the Damian McBride affair. The idea of pre-empting the inquiry on expenses by the Committee on Standards in Public Life by rushing out the Government's own proposals was under discussion before the "smeargate" scandal.

But Mr Brown couldn't resist the attempt to play politics. He resisted the all-party approach demanded by David Cameron and Nick Clegg and dropped his proposals on them to try to win some brownie points with the public. Labour's private polls show that MPs' expenses are of much more concern to voters than smears, since they think all parties attack their rivals. Although questionable expense claims are not confined to Labour MPs, they are liable to get the most flak.

The Brown proposals should make the system fairer and better. Whether the Prime Minister gets any credit is another matter. Voters don't normally say "thank you".