Waistlines of girls starting secondary school are more than 8cm larger than those of their counterparts 30 years ago, a study released today shows.

Their male classmates have waistlines nearly 7cm bigger and chests nearly 8cm bigger than 11-year-old boys three decades ago, according to Shape GB's National Childrenswear Survey.

The part publicly-funded survey is based on data from more than 2,500 children aged four to 17, who were measured with 3D body scanners in 2009-10.

The results show how children's' body shapes have ballooned since the last major survey, which was released by the British Standards Institute in 1990 and based on measurements taken from more than 8,300 children in 1978.

An average 11-year-old girl today is 148.78cm tall, compared with 146.03cm in 1978 - an increase of 2.75cm or 1.88%.

But her waistline is on average 70.2cm, the Shape GB survey found, compared with 59.96cm in 1978.

Because the 3D scanner does not compress the skin like a tape measure does, and the scanner also measures the small of the back, it produces width measurements around 1.9cm larger than a tape measure.

Even accounting for that difference, the average 11-year-old girl's waist has increased by 8.34cm or 13.9%.

Today's results put her hip measurement at 81.78cm, compared with 77.81cm in 1978, and chest at 78.4cm, compared with 71.31cm in 1978.

The average boy of 11 now stands 148.18cm tall, up from 144.63cm in 1978 - a 3.55cm or 2.45% increase.

His chest is 78.45cm, compared with 68.76 in the 1978 survey. When the differences in measuring method are accounted for there is still a 7.79cm, or 11.33% increase.

His waist has also expanded, from 61.49cm on the average 1978 boy to 70.02cm today, and his hips are 80.21cm, compared with 73.22cm in 1978.

Select Research, the company who managed the survey, said the scans, which recorded nearly 200 different measurements per child, also showed that boys and girls' body shapes differed before the age of seven, contrary to many retailers' assumptions.

They said that many clothes currently labelled for five-year-old boys were based on them being 110cm tall, while the data shows the average as 115cm.

The Shape GB data is being used by sponsoring retailers Next, Monsoon, Shop Direct and George at Asda to design clothes.

It is also to be used in the development of a 'Body Volume Index' (BVI) for children as an alternative scale to Body Mass Index (BMI), which relies on simple height and weight measurements.

Richard Barnes, MD of Select Research, said it was too early to draw conclusions on childhood obesity trends from the data.

He said: "The increases in waist circumference since 1978 show that children have got bigger. However, increases in height and chest size show that children in the UK have grown over the years in many ways.

"Using BMI to measure obesity in children should not be relied upon as an accurate indicator of risk to health as both components, height and weight, are variables.

"Measuring body shape in 3D and where a child's weight is distributed may provide us with new insights on the actual risk to health and change perceptions of what health interventions are required.

"Shape GB is a survey for retailers, but we will be using the data in due course to develop BVI thresholds for childhood obesity."