It is news that will cheer the heart of every tousled-haired, dirty finger-nailed, black-kneed kid around. William Brown has finally won. Dirt is good for you. A survey by the Institute of Child Health in Bristol University has found that grubby children may be their mothers' despair but they are in fact healthier.

Scientists have discovered that children who bathe daily (and wash their hands more than five times a day) are 25 per cent more likely to have asthma than their dirtier friends. And those who bathe least are the healthiest of the lot. The explanation that the ICH have come up with for this is that washing at an early age may have a direct effect on the child's immune system, leaving them more vulnerable and sensitive to allergens.

Hurrah say a zillion adolescent boys who spend hours avoiding the bathroom - until of course they discover girls and have to be prised out of there. But to be honest I don't think it needed a survey of 14,000 children in the Bristol area to prove clean children pick things up. It's a problem all too many mothers will be familiar with - the Nitty Nora Syndrome. Send your children to school with shining clean hair and you can guarantee they'll come back with head lice. Meanwhile the disgusting oiks down the road are still nit-free.

But history and literature could have taught us the danger of obsessive washing. The Roman empire did absolutely fine, conquering most of Europe and seemingly invincible until they started concentrating on Roman baths,and then suddenly it was Nero fiddling while Rome burned and making his horse a senior member of government. The other famous bather of the ancient world is of course Cleopatra, who it was said liked bathing in asses' milk for her complexion. The practice may have made her one of the most famous lovers in history but it clearly lost her the kingdom.

Cleanliness is not necessarily next to godliness. As 1066 And All That puts it, one of the cleanest kings of England was Bad King John who "demonstrated his utter incompetence by losing his Crown and all his clothes in the Wash". If he'd just fished them out of the linen basket to see if they'd do another day, the whole tragedy might have been averted. The book also darkly hints that the Order of the Bath was seen as an extreme form of torture in the Middle Ages.

Cleanliness has of course not had the best press when it comes to psychological matters. Think for example of Lady Macbeth. It's popularly been assumed that her sleepwalking and obsessive handwashing springs from guilt over Duncan's murder. Sadly it's more likely the spur was that Lady Macduff might be passing rumours that the new queen has dirty fingernails, which is why she wails that "all the perfumes of Araby will not sweeten this little hand". (It's now also believed that Ophelia didn't commit suicide but lost her balance after over-vigorous application of a loofah during some extra-mural bathing).

No, a little bit of dirt did no one any harm, as Just William can testify. While his arch enemies the Hubert Laneites were languishing on their beds sick with only an improving history book to keep them company, William and the Outlaws were out saving the day, getting five shilling rewards and munching through endless slices of layer cakes. A smattering of grubbiness is a small price to pay for what sounds like a vastly more exciting life.