A national food policy should be put in place to help combat obesity and improve the environment, the Liberal Democrat conference heard today.

Lady Miller, Lib Dem spokeswoman for the environment, food and rural affairs, announced that under a Liberal Democrat government, the first national policy on food would be delivered in Britain, overseen by a dedicated cabinet minister.

The policy would not only target nutrition to deflate rising levels of obesity, but also serve the purpose of improving the environment by encouraging greater consumption of local produce.

Citing a recent pilot scheme within the Co-op grocery chain, which is labelling foods clearly for consumers and backed up by fair trade policies, Lady Miller said such good practice would become spread nationally under the Liberal Democrats.

"It's not just a few of us who are worried," she told the conference. "People have become conscious that something is wrong in a big way. The concern about what to eat and what not to eat is enormous. You are what you eat."

"Food for life" targets would be established to ensure schoolchildren received proper nutrition, including 50% of ingredients being drawn from locally sourced produced.

Lady Miller pointed the finger at the Conservative party for the poor diets in today's schools which lead to poor concentration and hyperactivity, after the former government "cut school dinners, closed school kitchens and sacked school cooks", she said.

"At a single stroke they turned a generation away from eating a midday meal prepared with prime ingredients into a generation who ate snack food on the run. Vending machines filled the hunger gaps that inevitably appeared and children's moods swung on sugar highs and hunger lows."

In a bid to increase reliance on local, fresh produce, local authorities would be expected to provide communities with a "range of retail opportunities" through planning policy statements.

"Look at our environment," Lady Miller said. "Fertilisers and pesticides polluting rivers in coastal waters. Look at the energy wasted hauling food hundreds or thousands of unnecessary miles."

Speaking after the debate, delegate Cyd Lee, from Wiltshire and Chippenham branch, said the policy was in touch with the public mood: "It is workable but it will take some time, because businesses are always very slow to switch on to what the public really, really want."

Simon Goldie, from Islington, said: "As an aspiration it is very good because we have such problems in health."