Leading article: Many allowances, little accountability

So the Metropolitan Police have decided not to proceed with their investigation into the financial affairs of Derek Conway MP. Metaphorically throwing up their hands in despair, they said they could not pursue an investigation because Westminster did not have a system to account for MPs' expenses properly. This situation, they said, would "undermine the viability of any criminal investigation leading to a prosecution". In other words, it would be hard for any prosecutor to make a charge stick, because what was permitted to MPs in the line of expenses was so very poorly defined.

Now some will doubtless think Mr Conway a lucky man to have got off this particular hook so easily. He might not agree. Having lost the party whip, committed himself to standing down at the next election, and become a figure of national resentment, he has found himself condemned in almost every court but a court of law. In pointing out the total lack of any system governing MPs' expenses, however, the police may perversely end up doing Parliament a favour, by pushing it to devise one.

So far, voters have learnt in dribs and drabs what MPs can claim over and above their salary: expenses for a second home (which may be chargeable as their first, if that makes financial sense); a whole wedding list of fixtures and fittings for said home, pegged to John Lewis prices, and sums up to £250 (now £25) without a receipt. Oh yes, and they can employ sundry relatives for clerical and research duties, without declaring that they are actually members of their family. It was Mr Conway's rather generous interpretation of that provision that got him into difficulty.

This plethora of allowable expenses puts a rather different gloss on MPs' complaints about their salary – which for some is clearly more in the way of pocket money. And even if there was a time when wealthier MPs expected to fund themselves, and poorer ones were discreetly helped to maintain an appropriate lifestyle, the time for such noblesse oblige is gone.

One result of this inquiry into expenses must be a proper, published code of allowances. There may also be an argument for adjusting the ratio between an MP's salary and allowances. Whatever changes are recommended, however, they should be designed to foster clarity and accountability. This is the very least that taxpayers have a right to expect from their MPs.