There are no rules when it comes to sizing. The British Standards Institute (BSI) came up with guidelines more than 20 years ago, but the industry prefers to make it up as it goes along. A dress size 12 in Next might be a 10 in Marks & Spencer, something quit different in Gap. And what little scientific research into shape and size the industry has was conducted in 1951. What this means is that retailers are working with evidence supplied by the clothes giant Marks & Spencer, the only company to have kept any records. In 1920, for instance, the average woman was 32-20-32. By 1960 she was 34-24-33. By 2000 she had, apparently, swelled to 36-28-38. Bust and hips have increased, but the waist has grown by a disproportional 8in. No wonder that two years ago, after conducting a study of 2,500 women, M&S decided that its new average British female was a size 14. Last autumn saw the launch of an advertising campaign featuring the voluptuous model Amy Davis, size 16, running naked across a hilltop shouting: "I'm normal."

Now science is aiming to take the guesswork out of what will fit Amy and her 59m countrymen. Last summer saw the launch of the National Sizing Survey, the most accurate study of body shape ever conducted in Britain. Set up with £1.2m from the Department of Trade and Industry, with an extra £2.2m from a consortium of retailers including Great Universal Stores, the John Lewis Partnership and BHS, and supported by several universities, it aims to provide the latest data on the human form.

Using the latest American technology in 3-D body-scanning, the study measured 10,000 men and women of all ages and ethnic groups in research centres across the country. Stripping down to their underwear, the volunteers stepped into booths containing four sensors. In under 12 seconds, bars of white light gathered more than 150 measurements, including inside leg, wrist and upper arm, forming what is known as a "point cloud". A computer generates a 3-D image, and you end up looking a bit like Spider-Man.