A majority of Britons will be obese within 25 years because so many people are leading such unhealthy lives, warns a new report commissioned by the government. It concludes that record numbers of people will die from diabetes, strokes, heart attacks and cancers.

The inquiry by an epidemiologist, Professor Klim McPherson of Oxford University, is intended to influence government policy on obesity, which most experts describe as timid and ineffective. It was commissioned by the Department of Trade and Industry as part of its Foresight series of research projects into how the major challenges facing the country in the next 50 years can be tackled.

Unless people's lifestyles change:

· The cost to the NHS of treating obesity, currently £2bn, could soar as chronic overweight imposes ever greater healthcare burdens;

· The number of people with Type 2 diabetes, now 1.9 million, may rise up to ten times, leading many to have a stroke or heart attack, go blind or need to have a limb amputated;

· The UK could overtake the United States, where an estimated one third of people are obese, as the nation with the greatest percentage of citizens with a Body Mass Index of over 30 - the definition of obesity;

· Obesity-related cancers will rise;

· Life expectancy, which most experts have predicted will keep rising, could start to fall again because of the sheer scale of obesity.

Eight per cent of adults were obese in 1980, but by last year that had risen to 23 per cent of people in England. Using existing data from sources such as the Department of Health's Health Survey for England, McPherson and his team have predicted the number of people who will be obese in each social class and each region of in each year between now and 2050, with the figure passing 50 per cent of the population in 2032. Tim Marsh of the National Heart Forum, an alliance of more than 50 health and medical organisations, said the findings were frightening. 'People talk about an obesity time bomb but many argue that it has already exploded,' he said.