Britons' waist sizes have risen inch by inch. How do you measure up?

More Britons than ever are piling on fat around their waists and risking serious health problems such as heart disease, according to a new study.

A rapidly increasing number of people have a waistline that measures more than half their height, researchers have found, and that spells trouble.

More than 17 per cent of males and almost 12 per cent of females are above the waist-height ratio danger limit - a dramatic increase on measurements from the 1970s. The findings will come as a shock to many people who previously did not regard themselves as overweight.

The study, to be published in the International Journal of Obesity this week, provides even more evidence than previous weight-related studies that Britain is heading for a health crisis. The vast majority of those focused on the Body Mass Index, which measures overall weight against height.

The latest survey measures our expanding waistlines; waist circumference is particularly significant because a build-up of fat around the abdomen is more dangerous than on the thighs or the bottom.

The research, conducted by obesity experts at London Metropolitan University, makes particularly grim reading for women. Even though more men bulge over their belts, the percentage of the female population with big waists is increasing faster.

"This shows that specifically central or upper body fatness has increased, perhaps to a greater extent than overall fatness," said the report's authors. "The fact that this increase has occurred over a much shorter period of time in females is even further cause for concern, and most likely reflects gender differences in diet and physical activity during this period."

The problem is particularly pronounced in children, and scientists warn that they are storing up trouble for the future. Children's average waistlines have expanded by about two clothing sizes over the past 20 years. Overall, young waistlines are 1.6 inches larger than they were in the 1980s.

Dr Mary Rudolph, a paediatrician who conducted earlier research on the issue, said: "It is particularly concerning because we know that in adults an increase in fat around the waist is associated with cardiovascular disease." Large waistlines have also been linked to diabetes, a disease experts say will affect three million people by 2010.

Among those stunned to discover that she was in the waist-height ratio danger zone was Sue Fitzsimon, 30, an office administrator who lives in London. She is 5ft 6in tall and has a 33in waist. "By strict medical reckoning my waist size of 33 makes me clinically obese for my height," she said. "I find that insulting, as I think of myself as fairly fit. I don't go to the gym regularly but I do walk and jog occasionally.

"I try not to worry about it too much, but as women we are surrounded by images of thin women. Even mature women think they should have the waists of 18-year-olds.

"My friends do talk about other women's sizes around the dinner table. We have a female friend who we are always laughing about who eats too much cheese and drinks too much beer."

Kelly Garner, 29, a financial adviser from London and also 5ft 6in, has a waist size of 31in - only two inches smaller than Ms Fitzsimon's, but the right side of the waist-height divide.

"My weight has never been an issue to me," she said. "People worry too much about their waist size - I've known people who agonise about it. Sometimes I feel a bit insecure when I see ultra-thin models, but I think women will always worry about their weight while television and magazines go on and on about size and diets.

"Women are their own worst enemies as well - they are always judging each other for how they look. But, obviously, it is good to be healthy."