A cocktail of rotting supermarket vegetables and sewage is to be used to generate electricity.

Yorkshire Water's Marley works, at Keighley, is at the forefront of the nationwide project, in a partnership with Asda.

Lorry loads of past-their-sell-by-date vegetables and other degradable food -- like bread -- will soon be arriving at the sewage works to be turned into methane gas.

Yorkshire Water scientists have come up with the idea to mix the rotting food with sewage sludge to create biogas.

A small-scale experiment has been taking place at Knostrop sewage works, in Leeds, but now scientists want to prove it can work on a bigger scale -- 40,000 times bigger.

If it proves to be a success, the system could be snapped up nationally.

Issy Caffoor, who heads Yorkshire Water's research and development unit, said: "We believe this is the first time a combination of old fruit, veg and bread have been mixed with sewage sludge to create biogas and an organic-rich fertiliser."

Yorkshire Water process engineer Tom Taylor said the process was unlikely to generate enough electricity to sell to the National Grid, but it could be enough to make the plant self-sufficient.

Other benefits were that the amount of rubbish going into landfill sites was being reduced and that food waste was being used to create power. The treated sludge also produced an organic rich fertiliser for agricultural and horticultural uses.

Dr Ben Purcell, from W S Atkins, the company monitoring the pilot study, said: "If the trials are a success and the concept is adopted on a bigger scale, the amount of waste transported to landfills will be significantly reduced, and also the amount of waste recycling for beneficial use could be significantly increased."

Mark Shayler, Asda's environmental manager, said: "Not only does the scheme make sound environmental sense, it also gives us the opportunity to make savings on the cost of sending waste to landfill sites."