THROUGHOUT the generations, children's books have often shared a common character - the fat child.

He can be found in many of the most popular novels, from Billy Bunter through to Harry Potter. He is portrayed as being mean, greedy and unpopular.

Now, a Worcester academic has claimed this demonisation of overweight children could be affecting the way young readers perceive each other.

"Authors need to be careful about using such a stereotype and the way it affects the thinking of their young readers," says Professor Jean Webb.

"It's a delicate area and you must not marginalise particular groups."

Prof Webb is the director of the International Centre for Research in Children's Literature, Literacy and Creativity at the University of Worcester. Her research into children's novels and its links to child obesity reveals more than 100 years of negative stereotypes.

"The model for the characterisation of the English fat child begins back in the 19th century with the Muscular Christianity movement, which was linked with Christian Socialism," Prof Webb says. "Muscular Christianity emphasised masculinity, and healthy living."

Prof Webb said many of the great writers at the time, including GA Henty, Charles Kinglsey and Thomas Hughes, used young, athletic boys as their heroes, such as Tom Brown in Tom Brown's School Days. This, she says, was all about instiling ideals into young minds about what it was to be manly and popular.

"This hero is athletic and sporty and, one would deduce, not overweight," she says. "The stereotype of the hero has been established. In Tom Brown's School Days the weakest character is thin, sickly and effeminised and has to be protected by the hero Tom Brown.

"This model of heroism dominantly continues and sets up oppositional stereotypes, the most well-known one in the UK being Frank Richards' character Billy Bunter from the Greyfriars School Stories."

Many parents will remember the character Billy Bunter. He is overweight, greedy, a spy, lazy and cowardly. He was always the butt of the jokes in the popular stories.

And the theme continues in William Golding's Lord of the Flies with the character of Piggy.

Piggy is also overweight, has weak eyesight, asthma and is bullied. Moving in to the 1950s in The Lion, The Witch And The Wardrobe, the character of Edmund is slightly overweight and is tempted by the offer of Turkish Delight which ends up leading him in to trouble. In the 1970s, Roald Dahl's Charlie And The Chocolate Factory features Augustus Gloop, the fat boy that gets stuck in the shoot through his own greed. "There are so many examples through the generations," says Prof Webb.

"Fat children are always ridiculed. It even continues into the present day with JK Rowling's Harry Potter books. Here Dudley Dursley, Harry's human cousin, is overweight, badly behaved and spoilt by his parents.

"All of these characters are presented with being fat as an outward symbol of their dysfunctional personality, negative values and general unlikeableness."

However, Prof Webb said times could be changing with the publication of such children's books as Catherine Forde's Fat Boy Swim and Chris Crutcher's Staying Fat For Sarah Byrnes.

"In these books, the authors represent the fat characters in a different way," she says.

"The overbearing image of the 19th century hero is being balanced by the positive portrayal of fatness. Fat Boy Swim is not an irresponsible celebration of the overweight hero, for there are the associated health problems. Being overweight is thus presented as a physical problem for which there are pragmatic solutions."