A French supermarket chain has taken out full-page newspaper advertisements denouncing sharp price rises in popular foods, including camembert, triggering a serious rift between producers and retailers.

The unprecedented move by Leclerc has led to insults and lawsuits and thrown President Sarkozy’s Government on to the defensive over a law that prevents retailers from negotiating prices with their suppliers.

Anger over the price of camembert began when Lactalis, the French dairy group, which is Europe’s biggest cheesemaker, said its products would go up by an average of about 15 per cent.

President, its most popular camembert, would rise by almost 19 per cent, it told retailers.

The company, which makes more than half the 120,000 tonnes of camembert produced every year, said that it had been forced to pass on the rising cost of milk, which has also hit Dairy Crest in Britain.

But Michel-Edouard Leclerc, the chairman of Leclerc, described the price rises as “scandalous”. In a series of advertisements, he also criticised increases of 32 per cent for pasta, 23 per cent for eggs, 15 per cent for jam and 15 per cent for Aquarel, Nestlé’s mineral water.

“These rises are abusive,” the advertisements said. “Industrialists are using the rise in the cost of raw materials as a pretext to get rich. It is scandalous.”

Mr Leclerc added: “It is absurd. I do not deny the importance of the rise in raw materials, but I contest the scale of the price rises imposed on us by industry. The cost of the raw materials is often derisory compared with the finished product. Nothing, therefore, can justify such rises.”

With other French supermarket groups, such as Carrefour and Auchan, throwing their weight behind Leclerc, Nestlé responded by saying it would reconsider the price of Aquarel. But Lactalis and other suppliers were outraged.

However, a spokesman for Lactalis said that the company had no choice but to raise the price of the celebrated soft cheese that is produced in Normandy. “Camembert is 98 per cent milk and we cannot do anything else. On October 1, the price of milk paid to producers was 20 per cent higher than the average price for the year. The price of President must go up,” the spokesman said.

Jean-RenéBuisson, the chairman of the French National Agro-alimentary Industry Association, described Leclerc’s campaign as “demagogic”. “It is a useless provocation,” he said, adding that the association’s lawyers had been told to draw up a lawsuit in an attempt to stop the advertisements.

However, the camembert price controversy is seen by many observers as a prelude to a wider conflict over a uniquely French law that gives retailers little control over the price of the goods that they sell.

The legislation – designed to prevent cost-cutting to protect small shops - forces supermarkets to accept the prices demanded by their suppliers under a take-it-or-leave-it format.

In practice, retailers get round the law by negotiating so-called “soft services” such as shelf space and promotional campaigns.

However, Mr Leclerc said that prices would fall if the law was scrapped, placing the Government in an uncomfortable position as it seeks to position itself in the middle ground between consumers and industry.

According to an opinion poll yesterday, the cost of living is the greatest issue of concern to the French.

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