Britons have the thickest waistlines in Europe despite being one of the biggest spenders on diet products, a survey has revealed.

Long working hours, eating "on the go" and a heavy drinking culture has meant Britain is losing its battle against the bulge.

The report, entitled Overweight Consumers and the Future of Food and Drinks, identified Britain as having the greatest problem with weight, with Germany in second place.

The Datamonitor report, partly based on medical and government figures for 2004, found 40 per cent of the UK's population was overweight - the highest in Europe, and only 1 per cent lower than America.

A further 21 per cent were deemed "obese" in Britain and Germany, the highest percentage by far in Europe, and only second to America's 24 per cent.

John Band, author of the survey, said it was partly down to the UK's culture of "working hard" and "drinking hard".

"It is a reflection of the way Britain does not have the same tradition of cooking as people in mainland Europe. Lives in Britain are more 'on the go', with people working longer hours, having to maximise leisure time with higher drinking," he said.

He warned that the problem would continue to grow unless consumers were offered healthier and more convenient alternatives to junk food.

"If there is not a radical change in lifestyle, people will continue to become more obese and overweight," he said.

Experts predicted UK consumers would continue to raise their spending on diet products to reach £86 per person every year by 2009. In 2004, the diet food and drink market had a value of £4.6bn, a figure that is predicted to grow by 15 per cent to £5.3bn by 2009.

The Swedes and Dutch were found to spend the most on diet products in Europe, with Britain in second place, although Sweden and the Netherlands had a significantly lower percentage of overweight people (32 per cent and 30 per cent respectively).

Low-fat dairy products accounted for almost 40 per cent of expenditure on diet food and drinks, with a strong growth in "diet confectionery". Mr Band said the diet food industry was growing faster than the regular food and drink market.