THE National Grid, which is responsible for controlling power supplies, is urging all large energy users to allow supplies to be interrupted to forestall any threat of power blackouts at peak times next winter.

Power station capacity available to generate electricity has shrunk and the Grid has experienced critical shortages.

A serious alert in gas came last month and one in electricity last December, even though the winter was generally mild. Over the past few weeks the Grid has also sent out a series of warning notices over inadequate supply to encourage generators to produce power.

The 40 per cent collapse in wholesale electricity prices after the electricity trading system was changed two years ago has led to power companies mothballing power stations round the country. The Grid hopes to broker a large number of interruptible contracts whereby users will get payments for being prepared to have their supplies cut, and then additional cash each time they are actually cut. The Grid has always operated a small number of interruptible arrangements, but its new initiative of “turn down” contracts aims to expand this to take the strain out of the market.

The margin of generation available over what is expected to be needed has fallen from an average of 26 per cent two years ago to an expected 16 per cent average this year. At peak times, and when more generating plant is switched off than expected, the margin shrinks to much lower levels, triggering a system warning. In just three days last week the Grid issued six system warnings.

Last month gas supplies, which are also controlled by the Grid, fell into chaos when 150 big users, including more than 50 hospitals, had to seek alternative supplies because of an unexpected shortage. The coal industry is seeking talks with Stephen Timms, the Energy Minister, to stress the importance of mixed fuels in energy provision.

Mike Calviou, commercial frameworks manager for the Grid, said: “We are trying to ensure we have more options in balancing supply and demand. We have been working on this with the regulator and industry groups over the past few months.”

Bob Spears, chairman of the Utility Consumers Consortium and a long-time advocate of this approach to energy trading, said: “Faced with a possibility that the lights may go out in a totally unplanned fashion it is important to look at ways to cut supply when needed in a planned fashion.’’