Size matters – especially to a woman in search of a new dress. Finding one that suits can involve a dispiriting trawl along the High Street trying on garments whose labels bear little relation to their fit.

The failure of the major clothing retailers to adopt a standard system of sizes is blamed by shoppers – of both sexes – for turning what ought to be a pleasure into a chore. An alternative explanation is that it is the size of the shoppers that is the problem – not the size of the clothes.

To settle the issue, the first national survey of the size of the nation carried out for 50 years was launched yesterday. Size UK, backed by the Department of Trade and Industry and 18 major retailers, is seeking 10,000 male and female volunteers to provide a detailed profile of the changing national body shape.

It is the first time since 1951 that researchers have sought to measure body size. Volunteers are being asked to strip to their underwear and step into a body scanner which can provide 130 body measurements without having a shop assistant run a tape measure up their inside leg.

However, hand and head sizes have to be measured using conventional methods because the scanners are not sophisticated enough to provide accurate measurements of these parts.

Professor Philip Treleaven, head of computing at University College, London, forecasted yesterday that the results of the study, to be completed by Christmas, would show that the average woman's bust size had increased by two to three inches and the average waist size by three to four inches.

He said: "Better fitting clothes and standardising measurements between the retailers is the aim of the first national sizing survey. Londoners will be playing their part by volunteering just 10 minutes of their time. That's all it takes for us to see how the nation measures up."

The measurements will certainly be up, not down. Waistlines are expanding not only in Britain but in every country in the developed world. As prosperity grows so does girth.

Cinema and aeroplane seats have been steadily widened over the past 50 years to accommodate expanding bottoms and a rough guide to national income can be gained from the average dress or trouser size.

In Britain, 20 per cent of women are classified as obese, compared with the 8 per cent recorded in 1980. Among men, 17 per cent are obese compared with 6 per cent 20 years ago. More than a third of men and half of women are considered overweight.

People are also taller, men are more muscular and women more curvaceous – the product of better nutrition. Pictures of pigeon-chested youths from the 1950s compared with the young Amazons of today show how far and how rapidly the nation has grown.

Yesterday in the Size UK dressing room, where 90 female volunteers were expected, a group of three middle-aged women were waiting to be measured. One, who did not wish to be named said: "We're here because we find it very difficult to get clothes that actually fit properly. We're all individuals after all. Manufacturers take clothing measurements in other countries and don't adjust them for the fuller British figure."

Jane Doogan, 26, who has a generous bust but slim hips admitted she bought clothes that were too small for her. "I'd probably buy a smaller size if it was a dress because I'd want it to fit the whole way down my body. I'm bigger at the top than at the bottom. I can't get the right trousers, the legs are too short or the hips are too big."

Dissatisfaction with their body shape is not confined to women. Jenny Bougourd, a Size UK researcher, said men were equally self conscious. "The men don't complain about their bum shape like women do but they're very expressive about everything else," she said. "They're unhappy about the size of their thighs, their calves are too thin, they're not tall enough or their arms are too long or their legs are too short."

The survey will continue until 20 December in fashion centres at Southampton, Cardiff, Birmingham, Nottingham, Manchester, Leeds and Edinburgh. Interested volunteers can log on to or contact the organisers on 0870 7273 131.

How the world shapes up

Body shape is determined by a range of factors of which diet is only one. International comparisons show that genes, culture, physical activity and social attitudes all play their part.

Britons may be getting bigger ­ but they are far from the biggest. In the global league table, the UK ranks somewhere in the middle of the world's thinnest and fattest nations.

Within Europe, Sweden is the slimmest nation thanks to the popularity of muesli, skiing and a belief in physical prowess ­ reflected in the popularity of its sports clubs, which boast the highest membership in the EU.

The heaviest nation is Germany, where the popularity of sausages and Sachertorte, combined with a commitment to harness technology ­ thereby reducing effort ­ has seen the scales soar.

From the diminutive Chinese to the bulky Samoans, the variation in body shape is immense. In China, a largely rural lifestyle which makes heavy physical demands, combined with a low-fat rice-based diet keeps the population trim. In Samoa and the neighbouring Pacific islands, a large waist measurement is regarded as a symbol of high status and prosperity and, therefore, is seen as attractive.

There are also gender differences. Women tend to be fatter than men, a legacy of childbearing.

Despite the enormous international range in body shape, only about 20 per cent of the difference is attributable to genes. Animal studies show that rats given an unlimited quantity of palatable food will continue to put on weight until the food is restricted. Humans may be no different.

Estimates by the World Health Organisation's task force on obesity suggest that, by 2005, there will be about 26 million obese adults in the United States. On present trends, the entire US population will be obese in 35 years unless Americans curb their appetites.