He has championed the cause of healthy school dinners, leading the crusade against Turkey Twizzlers and chips with everything and extracting a pledge of £280m from Tony Blair to improve children's diets.

But Jamie Oliver's crusade to persuade a generation of children to eat their greens may carry a hidden cost: the potato industry fears it could spell the beginning of the end for the Great British chip.

Sales of oven chips have plummeted after the first series of Jamie's School Dinners, which is also blamed for a per-capita decline in the total consumption of potatoes, as shoppers switch to the pasta and rice dishes he championed.

As a result, the country's biggest oven-chip manufacturer, McCain's, which buys 12 per cent of Britain's annual potato crop, is launching a fight-back against the "myth" that the 35 per cent of British spuds turned into fries are bad for your health.

A £15m advertising campaign devised by Trevor Beattie emphasises the "natural" provenance of McCain's products, which suffered an 8 per cent fall in annual sales after the launch of Oliver's campaign.

The firm denies the new advert's soundtrack - an adaptation of "food glorious food" from the musical Oliver - is a reference to the high-profile TV chef. But spokesmen have attacked the decision by some schools to ban chips.

In a bid to prevent their product going the way of the Turkey Twizzler, McCain's have also launched a road show called The Potato Story. It will tour schools with "an interactive experience designed to educate children in a fun and engaging manner about where their food really comes from".

The British Potato Council, which represents the country's 3,100 potato-farmers, will launch a media campaign next month entitled "fact, not fiction". It will emphasise the healthy attributes of the £4bn-a-year potato industry. They say research shows British consumers believe, wrongly, that the pasta and rice dishes are better for you than those made from spuds.

"Almost all consumers think potatoes have higher fat content, and more calories, than rice and pasta," said a spokesman. "In fact, potatoes - and even chips - are the best in most categories. As well as a newspaper campaign, we will also tour schools, showing them how to incorporate potato products into menus without breaking the government guidelines introduced as a result of the Jamie Oliver show."

Within hours of BBC Breakfast reporting on a school in Leicester "banning" chips yesterday, McCain's issued a press release saying the policy was counter-productive. "As we are seeing in Leicester today and Rotherham last week, kids are now voting with their feet by leaving school to visit the chippy instead of staying on site to eat a hot meal that includes a healthier version of their favourite food," the company said,

Bill Bartlett, McCain's director of corporate affairs, added: "We are not attacking Jamie Oliver. In fact, we support the principle of his campaign, which is to provide healthy food to children. Our principal issue is that chips keep getting wrongly tagged under the headline 'junk'."

Now Oliver has stressed that his school dinners campaign is not "anti-chip". His nutritional adviser, Jane Clarke, said: "Chips are fine for lunch as part of a balanced meal. They are a good source of vitamin C, and starch and fibre. Jamie is absolutely fine with that.

"But when children are eating them every single day, or when they are eating them on their own, with maybe just a can of fizzy drink, then obviously that is a problem. With chips, as with almost all foods, it's all about balance."