James Adler, from London, is only 10, but he is reluctant to go to his friends’ parties. And it is not because he is shy. It is because he is worried they will not give him chicken nuggets, sausages or chips.

“Apart from peas,” says his father Andrew, “these are the only things he will eat.”

Parties are not the only nightmare scenario for a fussy eater. Holidays in France are hell. “We have to eat in awful restaurants where they will serve what he likes, or we have to eat separately. We can only eat together if we eat sausages and chips,” says Andrew.

He does not remember how the problem started, but it was a long time ago. “We used to give him the occasional pre-prepared meal because my wife never liked cooking. Then he got fussier and perhaps she gave in too easily. Now, if I cook him a shepherd’s pie, for example, he won’t eat it.

“So, after years of wasted time and wasted food, we give him what he wants. We are as strong as we can be with him without it being torture for everyone.”

Such a diet puts children at risk of high cholesterol, vitamin deficiency and, later in life, illnesses such as bowel cancer. And while James is thin, obesity in Britain has doubled in the past decade, thanks to the popularity of junk food. One in seven 15-year-olds and one in 12 six-year-olds are obese.

In the face of such statistics, the government wants to persuade children to eat healthily. Free fruit is being given to nearly 1m primary children at school break-times and clubs where pupils grow vegetables are being piloted in some schools. Breast feeding is being promoted, too, as it is less likely to lead to obesity in children than bottled milk. The Welfare Food Scheme, which used to provide low-income mothers with liquid milk or infant formula, is being switched to offer fruit and vegetables.

The Food Standards Agency has launched a public debate on the effects of food advertising on children. Last week health experts hit out at the use of sports stars such as Lawrence Dallaglio, the new England rugby captain, to promote fast food. In Dallaglio’s advert he is seen demanding 110% beef in his McDonald’s burger.

Celebrity chefs are joining the debate, too, with Jamie Oliver attacking the nutritional value of school meals and Antony Worrall Thompson campaigning against school buffets.

So how does a child learn to turn away from healthy foods? Jane Clarke, a nutritionist, says the problem often starts with jars of baby food that contain sugar and salt.

“It’s hard for mothers who have fed their children from these jars, because nothing they cook after that will be tasty. But they should be strict. Babies don’t need mashed potatoes with salt,” she says.

Annabel Karmel, the author of the children’s food bible Superfoods for Babies and Children, explains that babies have a sweet tooth because breast milk is sweet. But, she says, continuity can be achieved with sweet potatoes, sweetcorn or mashed banana, rather than baby pots.

“Parents who give their children natural, fresh food right from the very beginning, are the best off later,” she says.