Benjamin Franklin once warned politicians to be wary of the little expenses for fear that a small leak will sink a great ship. He should have tried buying a plug on expenses here in Britain. The saga of the Additional Cost Allowances is now descending into farce. The credibility and authority of Parliament is falling with it.

The Prime Minister is often castigated for being slow to react so it seems harsh to criticise him for one of his more expeditious decisions. All the same, the decision in haste to appoint Sir Thomas Legg to conduct an inquiry means that a lot more MPs may yet get to repent at leisure. It is to Sir Thomas’s credit that he has not turned out to be a patsy of the politicians. But the arbitrary nature of his judgments seem to bear out the advice of the Chinese proverb: never write a letter while you are angry.

The Chancellor of the Exchequer has been asked to return a payment equivalent to just under half the cost of a chest of drawers. It could be no more absurd if he cut up his furniture and sent half of it back. Lord Mandelson’s gardening excess, we now learn, is £110 less serious than Nick Clegg's. Two weeks ago Sarah Brown told us that her husband Gordon was too messy. Now we discover he is, in fact, too clean, £12,415 too clean, to be precise. Labour MPs in poor constituencies would be passed by Sir Thomas if they bought their local town hall — there being no limit on mortgage payments — but not if they kept on the cleaning staff.

You might be tempted to conclude that you couldn't make this stuff up if that weren't exactly what has just happened. Actually, it's worse even than that. The accusation throughout was supposed to be that the MPs did make up their own rules. In fact, they've hired Sir Thomas Legg to make them up for them and he has added the cunning twist that they should apply from a starting date of his choosing.

The application of retrospective criteria alone calls Sir Thomas’s verdicts into legal question. Despite the plausible view of the party leaders that MPs have no choice than to pay up at once, the natives are restless. Martin Salter, MP, has described the process as “monstrously unfair”; Bill Etherington, MP, has said he will not pay a penny back. Ann Widdecome, MP, has accused Sir Thomas of exceeding his remit. Norman Baker, MP, has added another concern: accuracy. Mr Baker was asked for additional mortgage documents even though he has no mortgage. It seems that, in the rush to report, basic errors have been made. A process that lacks legitimacy and draws arbitrary conclusions from questionable evidence is bad enough. The only hope for the reputation of Parliament is that it should be over and done with quickly. Unfortunately, this is barely the beginning of the end. The letter that Sir Thomas has sent to all MPs is provisional, a sort of opening gambit. Those MPs who do not simply pay up are being asked to respond to Sir Thomas with their comments and he will return with his considered verdict.

As if that is not enough already, only then will Sir Christopher Kelly, the chairman of the Committee for Standards in Public Life, publish his report on the whole expenses episode which, after an interminable wait, really needs to set the matter to rest.

In fact, MPs are kidding themselves if they think any committee of inquiry will do that job. There is only one way to purge this issue and it has the great advantage of being immediate. The Prime Minister could call a general election. Rather than a succession of faceless bureaucrats standing in judgment, rather than the old boys’ club putting up a series of hanging judges to decide on hanging baskets, it is surely time for the people to be permitted their say.