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Families in England are to be offered £250m in vouchers in a bid to encourage them to eat healthily and exercise.

Food vouchers, nutritional advice and discounted activities are all part of Change4Life's "Great Swapathon".

The food and fitness industries are paying for the tokens, as part of the government's plans to involve business in the promotion of healthy living.

But food policy experts have previously raised doubts about involving big firms in public health campaigns.

By filling in a questionnaire on the , people can get access to £50 vouchers giving money off healthier food and activities.

The government says £250million of vouchers are being made available as an incentive to get people swapping their unhealthy habits.

Four million £50 voucher books will be on offer through the News of the World and Asda stores.

One million will be available through local businesses which have signed up to Change 4 Life, the government's health-promoting initiative.

Individuals and families can also access recipes for healthier snacks and meals, as well as nutritional advice on the website.

Companies supporting the government's scheme include Asda, Birds Eye, Unilever, Nestle, Mars, Warburtons and Weight Watchers.

Health Secretary Andrew Lansley said: "It's a great example of how government, the media, industry and retailers can work together to help families to be healthy.

"The healthy option isn't always the cheapest option so it's a really important step to be able to offer £50 off healthier foods, drinks and activities."

But food policy experts have previously questioned the wisdom of allowing big brands to become involved in telling the public how to eat more healthily.

Tim Lang, professor of food policy at City University, said: "I'm nervous if big companies are put in charge of public health - that's not to say they can't be good for public health - but if they are centrally involved in delivering it.

"I think that history suggests we need to set frameworks, level playing fields in which they then operate.

"I don't like them controlling it."

Professor Dame Sally Davies, the interim Chief Medical Officer for England, said: "The new year is a great time to think about making some small changes to be a little bit healthier. My simple tips are to be a bit more active and eat a little more healthily.

"Ideally we should be doing 30 minutes of exercise five times a week - or an hour a day for children.

"Exercise doesn't have to be painful - you could take the dog for a walk or play with your kids in the park. Anything that gets your heart pumping.

"And we should try to eat five portions of fruit and veg every day."