FAST-FOOD chains including McDonald’s, Burger King and KFC are to be sued by the state of California for not warning consumers about a potentially cancer-causing agent produced when potatoes are deep fried.

The lawsuit is the first of its kind in the world and could result in health warnings on French fries, or at least on the walls of restaurants.

It says that nine defendants, including H J Heinz, which makes Ore-Ida frozen chips; Procter & Gamble, which makes Pringles crisps; and Kettle Foods, creator of Kettle chips, are violating California’s Proposition 65, which requires warnings when consumers are exposed to known carcinogens.

“I am not telling people to stop eating potato chips and French fries,” said Bill Lockyer, the California Attorney-General. “But I and all consumers should have the information we need to make informed decisions about the food we eat.”

The agent is acrylamide, traces of which can also be found in breakfast cereals, breads, olives, asparagus, coffee and even prune juice. Mr Lockyer is seeking labelling only of potato products.

It was discovered in 2002 that potatoes cooked at high temperatures contained low levels of acrylamide. Some scientists have discounted its potential toxicity, but tests are being done by the Food and Drug Administration.

A consumer group began lobbying California in June to take action. At the time Frito-Lay issued a statement saying that its food safety standards were “very stringent”. Procter & Gamble said that researchers were still investigating issues raised by the 2002 study.

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