Two out of three Britons are so inactive that they risk a wide range of chronic and disabling illnesses, the Government's Chief Medical Officer is to warn.
The scale of the descent into indolent, sedentary lifestyles - with most people failing to do even the minimum recommended exercise - will be laid bare by Sir Liam Donaldson in the New Year.
Donaldson will urge the public to build bursts of activity into their daily lives to protect their health. He will spell out how even chores such as DIY, housework and gardening can increase energy levels, and that playing sport and going to the gym are not the only solutions.
His shocking conclusions will lead to a sustained Government campaign to reduce 'couch potato' behaviour and soaring rates of obesity, which threaten an epidemic of cancer, diabetes and heart disease. Ministers will announce an action plan in April to try to reverse the slide.
A media and advertising blitz is being planned, which will include characters in popular television programmes such as Coronation Street taking up healthy pursuits such as gardening. ITV is already planning a 'Britain On The Move' publicity drive to promote walking.
Donaldson's report, expected in February, will show that a majority of the population fails to do the amount of activity which the Government and World Health Organisation say is necessary for good health. He will point out that up to half of boys and up to two thirds of girls aged from seven to 16 do not meet the targets, and that up to two-thirds of adult men and three-quarters of women are just as inactive.
Ministers have privately encouraged Donaldson to make his call for action as uncompromising as possible to help them avoid accusations of 'nanny state' interference. Nine Whitehall departments are involved in producing the action plan.
Professor Ken Fox, a social psychologist at Bristol University, said: 'We have been conditioned since Victorian times to find easier ways of living. We want lots of dishwashers and lots of cars.
'There needs to be a serious shift in attitudes, so that exercise is no longer seen as the enemy but as the friend.'
Official advice is that adults should do 30 minutes of 'moderate activity', such as brisk walking, at least five days of the week, and that under-18s take an hour's exercise every day.
Ministers have seen research showing that the nation is divided between 36 per cent who play sport regularly or occasionally and 64 per cent who like 'putting their feet up'.
Health and fitness experts have formed a pressure group, Move4Health, to encourage Ministers to promote exercise. Its founder, Felicity Porritt, said: 'We are prisoners of our environment and live in a take-it-easy culture where the car is king at the expense of pedestrians and cyclists.'
Whitehall is arguing about who will pay to promote increased activity levels. The Department of Health spends less than £1m per year of its £65 billion budget to do that, but is under pressure to see exercise as preventative medicine and spent much more.