The chairman of ScottishPower's owner has become the latest boss of a "big six" energy producer to warn that Britain faces looming power shortages.

Ignacio Galan, chairman of Spanish firm Iberdrola, ratcheted up the pressure on the UK Government after Ian Marchant, chief executive of Perth-based SSE, said there was a "very real risk of the lights going out".

Mr Galan called on the ministers to provide more details about its proposed energy-market reforms if new power plants are to be built in time to avoid energy shortages in the next few years as older power stations are closed.

"Although the Energy Bill currently going through Parliament is in the right direction, greater clarity of detail is needed if investment in new power stations is to be speeded up," he said.

He noted industry regulator Ofgem has warned that if no new plant construction begins now, there could be shortages in 2015.

Centrica, owner of Scottish Gas, said it would not build any gas-fired power stations for at least four years due to uncertainties about pricing.

ScottishPower plans to close a quarter of its power plants by 2020. Earlier this month, its coal-fired power station at Cockenzie in East Lothian was shut down.

It wants to open a new gas-fired station on the site, but said it would not commit to this until it was clearer what the market would look like.

Meanwhile, the Institute of Directors has called on ministers to ensure the UK increases its production of gas after it emerged Britain was just days away from running out. The wholesale price of gas jumped to a new high after a technical fault shut the main pipeline from Europe, putting pressure on UK supplies.