Forget Swiss ball sculpt, pilates, and other gym fads; if you want to get fit, what you really need to do is a spot of vacuum cleaning. That's according to the government's chief medical officer, Sir Liam Donaldson. He has drafted a white paper, physical activity and health, due out on Thursday, in which he will urge the British public to get off their lardy backsides to do a spot of housework and gardening. These activities will be touted as a real alternative to going to the gym. Not only can you get fit and pay no membership fee for the privilege, but your house will look great.

Unless you have been out of the country for the past few years, you will know that we are facing a big rise in obesity. One in four men and one in five women are obese. Each year, 9,000 people die prematurely in Britain as a result of being overweight. Type 2 diabetes, which is linked to obesity, is increasing among children (usually, you wouldn't expect to develop it until middle-age), and binge drinking is a growing problem. As a nation, we are going to the dogs. We need to get active. Health specialists have been telling us for ages that we must get at least 30 minutes of exercise a day, five days a week. Not only will it keep our weight in check but it can also lift mild depression, strengthen bones, and stave off heart disease.

In the report, we are told that cleaning windows, cutting the grass and vacuum cleaning, all count as moderate exercise. As a comparison, golf, brisk walking and doubles tennis also count as moderate exercise. If you do 30 minutes of moderate household chores a day, five days a week, your fitness will improve. But, be warned, not all household activities fall into the moderate category. Don't think you can get away with 30 minutes of ironing and dusting a day. These count merely as "light" activities and are no healthier than a slow dawdle down to the pub. Unfortunately, no household chores count as vigorous exercise, so don't expect to be competing in the lawn-mowing Olympics any time soon.

The health secretary, John Reid, recently called for a public debate about how we can improve the country's health. These include discussing whether we should ban smoking in public places and restrict junk food advertising. Reid feels that efforts to reduce levels of obesity have been concentrated on those already involved in sporting activity. Now it's time to find alternative ways of shedding the nation's weight. But tidying up your house?

Jason Behenna, who has been in the gym business for more than 15 years says, "If a person does no exercise whatsoever, then possibly you may be able to lose a bit of weight - in conjunction with a controlled or calorie restricted diet. But in terms of your average household work, you have to do enough of it constantly to warrant any kind of physical change. In my personal opinion, this [the report] doesn't sound very scientific."

Sean Ganser, a keen gym-goer from London says: "I know what exercise is. When I finish on the benchpress, my arms are shaking ... you won't get that from a vacuum cleaner."

If what Donaldson is saying is correct, domestic cleaners must be in pretty good shape. I asked Ali Gullen of Maxclean.co.uk whether he has a finely honed body. "It keeps me fit," he says, "but I'd prefer to go to a gym." And that's one rub - what domestic cleaner can afford to join a fitness club? There is a link between obesity and income. Roughly, the less you earn, the more likely you are to be overweight. Not many people earning a basic wage can afford the hefty annual membership most big-name gyms charge. For example, an annual membership to The Third Space in Soho, London costs £1,100 a year. People who can afford this sort of price tag can usually afford to pay someone else to clean their house.

Nigel Wallace, executive director of the Fitness Industry Association (FIA) and clearly a man keen to prevent a mass defection from the running machine to the ironing board protests, "Gym memberships start at as little as £15 a month and many leisure centres offer concessions for those on income support. Going to the gym doesn't have to be expensive and compares very favourably with other leisure activities such as going to the cinema, bowling, going to the pub, playing bingo or even watching a video."

Harm Tegelaars, chief executive of Cannons Health and Fitness, a fitness club chain, supports the government's commitment to make us healthier individuals. "The key is that people understand that low- and moderate-level exercise activities (mowing the lawn, walking an extra stop to catch the bus) should form the base level of physical activity," he says. "We can then build on these levels to help members get to the next level of achieving specific health and fitness goals. This may require more specific activity and often more vigorous exercise."

Wallace wishes that the chief medical officer had prescribed health clubs as part of his solution to a better national fitness regime. "Over 17% of the population are regular users of health and fitness clubs and centres," he argues - even if this would probably be dwarfed by nationwide vacuuming rates, were the Office for National Statistics to produce such a thing.

However you get your 30 minutes of moderate exercise each day, it will reduce your risk of heart disease by 50%. You may not shed the pounds or get a six-pack, but you will be healthier. If not visibly, at least internally.

I ask one of London's top gyms whether it would be adding vacuum cleaning classes to its list of activities any time soon. "I don't think so," says the spokesperson, "but should Donaldson wish to come and demonstrate his services on a weekly basis, I'd be more than happy to supply him with a vacuum cleaner."

So would the average punter prefer half an hour of household chores or half an hour at the gym? The verdict of Rob Farag, a man who does his own ironing and describes himself as being slightly overweight: "Neither."