Those accused include Masterfoods, which makes Mars and Twix, and the confectionery giant Cadbury Trebor Bassett. Burger King and McDonald's are continuing to offer large versions of their chips, drinks and sandwiches, despite pledges to phase out super-sizing.

Cath Dalmeny, a policy adviser with the Food Commission, a lobby group, said: "All these pledges have been nonsense. The manufacturers have tried to pull the wool over the eyes of the public at the same time as trying to get the Government off their backs, but what they have done is misleading. These products are still high in sugar, fat, salt and calories and are contributing to the obesity problem."

The food industry has come under huge pressure to reform its marketing and manufacturing practices or face stricter regulation and more stringent labelling rules as part of a government drive to cut obesity rates. Three-quarters of the adult population are now classed as overweight and one in five children aged 15 is obese.

Last year, the Food and Drink Federation (FDF) launched a seven-point manifesto for change, with promises to reduce levels of fat, salt and sugar in products. The manifesto also pledged to cut portion sizes and over-consumption and to work with the Government on clearer nutritional information.

Companies such as Cadbury attracted generous publicity by announcing the end of super-sizing. In a follow-up report yesterday, the FDF claimed it was making "real progress" on the commitments. In the brochure, Cadbury Trebor Bassett says: "[We] have withdrawn king-size portions." But a spokesman for the company later confirmed this referred only to king-sized bars of products such as Boost and Crunchie.

Privately, officials say that they will not take the industry's assertions "lying down", indicating manufacturers may yet face tough sanctions on advertising and labelling.