The UK faces widespread power cuts for the first time since the 1970s, according to the Government's own predictions.

Demand for electricity from homes and businesses is set to exceed the available supply within eight years.

The Tories accused ministers of putting their "heads in the sand" and risking leaving millions of people without reliable energy.

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Power rationing has not taken place in Britain since the 1970s, when a three-day week was brought in to preserve coal during a miners' strike.

The latest figures cast doubt over the Government's pledge that renewable sources can make up for lower output from nuclear and coal.

They were slipped out in an appendix to the Low Carbon Transition Plan, which was launched in July. The main document set out a target for "clean" technology - such as wind, wave and solar - to supply 40% of the country's power by 2020.

But the extra section suggests that there will be a shortfall by 2017, when the "energy unserved" level is predicted to reach 3,000 megawatt hours per year.

That would be equivalent to the whole of the Nottingham area being without electricity for a day.

By 2025 the situation is expected to worsen, with the shortfall hitting 7,000 megawatt hours per year.

That would be equivalent to an hour-long power cut for half of Britain over the course of a year.

Shadow energy secretary Greg Clark said: "Britain faces blackouts because the Government has put its head in the sand about Britain's energy policy for a decade. "Over the next 10 years we need to replace one third of our generating capacity but Labour has left it perilously late, and has been forced to admit they expect power cuts for the first time since the 1970s.

"The next government has an urgent task to accelerate the deployment of a new generating capacity, and to take steps to ensure that, as a matter of national security, there is enough capacity to provide a robust margin of safety."

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The looming power shortage is caused by the scheduled closure by 2015 of nine oil and coal-fired power plants, as part of ant-pollution measures.

Four existing nuclear power plants are also set to be shut, adding to the need for new sources of energy.

Mr Clark claimed that the scale of the blackouts could be three times worse than the government predictions.

He said some of the modelling used was "optimistic" because it assumed little or no change in electricity demand up until 2020.

It also assumes a rapid increase in wind farm capacity, and that existing nuclear power stations will be granted extensions to their "lifetimes", according to Mr Clark.