One Labour MP, Emily Thornberry, was sent a bath-plug in the post by a constituent angry that the home secretary Jacqui Smith had claimed 88p for one on her parliamentary expenses. Another Labour member, Alan Simpson, brandished a plug during a House of Commons debate, warning that a failure to tackle the big issues affecting people's lives had "degraded and devalued politics to the level of the bath-plug".

Farce or tragedy? It's both. Friday's embarrassing disclosures about the expenses claimed by 13 ministers, including Gordon Brown, inflict more bruises on Labour at a time when the party and its embattled leader are already on the ropes. But The Daily Telegraph's revelations will also do more damage to the image of politics as a whole. Public scepticism has become downright cynicism.

Labour was already facing a drubbing at the European Parliament and local elections on 4 June. Now things can only get worse. Nor will Tory and Liberal Democrat blushes be spared as more details are dribbled out over the next few days. The reaction of many voters will be a "plague on all your houses" on the grounds that all political animals have their snouts in the trough. "People have moved from apathy to antipathy," said Rob Hayward, an elections expert and ex-Tory MP.

A long-running expenses saga could dominate the June elections campaign. Worryingly, it could easily boost support for the far-right British National Party (BNP), which is trying to win its first seats in a nationwide election in the Euro poll. The revelations could be a timely gift to it. Was The Telegraph right to publish? The Telegraph has a public interest defence in that it needed to see the uncensored version – including MPs' addresses, for example – to work out the scams, such as the repeated switching from what is the 'first' and 'second' homes to maximise expense claims.

But the fact that at least three other papers turned down the goods tells us something. So far, there is no sign of corruption or ministerial resignations. It's a fair bet that disclosure of similar material in most countries on the continent would make The Telegraph's scoop look very small beer. The total cost should be kept in perspective. Commons accounts show that MPs' salaries, at present £63,000 (€70,000) a year, cost about £56m (€62.6m) annually, staffing allow­ances £55m (€61.5m) and the controversial "second homes" allowance only £11m (€12.3m). The housing payments have generated a disproportionately large amount of headlines because the rules are open to abuse.

Greedy MPs have milked the system for all its worth, but within the rules of the club. They were poorly policed by officials reluctant to doubt the honour of 'honourable members'. But that is no excuse.

Brown's instincts were right when he tried to bounce MPs into a snap decision on expenses reform two weeks ago. His plan to replace the £24,000-a-year 'second homes' allowance with a daily attendance payment could have limited the damage. If it had not been scuppered by MPs, they could have argued that they had (just) killed off the worst aspect of a rotten system.

Unfortunately for Brown, he tried to get personal credit for cleaning up the system, so didn't consult anyone first. If he had done, he might well have got a consensus for changing the 'second homes' payments. But he was outmanoeuvred by an alliance of opposition parties and Labour MPs upset by not being told about his plans.

The opposition to Brown's plan is symptomatic of the Westminster culture which spawned the expenses system. It dates from the 1960s and 1970s, when allowances were boosted so MPs' pay could be held down as governments preached pay restraint to the nation.

MPs, too mindful of their own pockets, have been painfully slow to change that culture, and the rules on expenses they fix for themselves. Many say it is "the system" that is wrong, not their claims, as if "the system" has nothing to do with them. It has everything to do with them.