By Laura Donnelly, The Telegraph Group Limited

London: Children's clothes sizes are to be changed to cope with a generation of bulging waistlines.

High street retailers plan to draw up new sizes, in response to the growing number of overweight and obese children.

Shops including Next, Asda and Monsoon are measuring 6,000 boys and girls amid an obesity epidemic which means one in three British children is now classed as overweight.

Manufacturers will use the results of the survey, using high-tech scanners, to decide how far to increase waist sizes and other measurements to allow for the expanding bulk of the average child. Most companies currently rely on statistics on children's sizes that were published in 1990, as the obesity epidemic was just beginning.

Asda, which sells the most children's clothing in Britain through its George brand, said it wanted to respond to the demands of its customers.

A spokesman said: "The size of children is changing, and like many retailers we are relying on measurements that were taken almost 20 years ago. We have done a lot to respond to customer demand but children are getting bigger and we need to respond to that."

A spokesman for Next said the retailer wanted to respond to the fact that the average child is "taller, broader, and bigger" as well as to changing fashions.

The number of obese children has risen by one third in the past decade. More than 30 per cent of children are now classed as overweight, including 17 per cent - 900,000 - whose health is at significant risk.

Children's clothes are normally sold by age ranges, such as 7-8 or 10-11, meaning parents of overweight children usually buy clothes intended for older and taller children.