Electricity prices could rise by as much as 20 per cent to pay for upgrades to the power network.

Paul Golby, chief executive of Powergen, said yesterday that the network would need to spend £50 billion to £70 billion as coal-fuelled power stations reached the end of their working lives.

Last week, Elliot Morley, the environment minister, admitted that electricity prices would rise about six per cent by 2010 to pay for a scheme that reduced carbon dioxide emissions.