Ofgem warned of UK blackouts because of the dwindling number of coal and oil fired power stations, which is hindering electricity generation (Reuters)

National Grid has warned that the threat of winter blackouts is dramatically increased as dwindled electricity reserves have left a narrow safety margin should the supplies run out.

There is just a 5% cushion of reserve supply of electricity for the UK to rely on if a particularly cold winter takes grip and demand soars. This is the lowest level of reserve supply since 2007, as the number of operating coal power stations plummets.

"Things will be tighter than they have been historically," warned Chris Train, network operations director at National Grid, reported The Telegraph. Train added that he did not think there would be blackouts in the UK because the country would import additional supply if it was needed.

At the end of 2012, industry regulator Ofgem warned in its annual Electricity Capacity Assessment that the closure of nine coal and oil-fired plants would slash spare generation capacity to 4% by 2016, down from the 14% that year.

EU environmental law has driven the closures, as member states are obliged to meet emissions targets and seek out cleaner sources of energy.

Energy Minister Michael Fallon has insisted that there will not be any blackouts in the UK, despite the supply-side challenges and growing demand.

"I can assure you the lights are not going to go out. The regulator Ofgem has got to make sure, with all the tools at its disposal - bringing some mothball plant back in action and back on line - that the lights stay on and they will," said Fallon in June.

The latest National Grid warning follows Labour leader Ed Miliband's pledge to freeze consumer energy bills for two years if he is elected in 2015.

Miliband was subsequently attacked by the industry, who said he ran the risk of blackouts by threatening the security of energy supply.

"We have a responsibility to supply this level of energy and that means buying it in at costs which are largely outside our control," said Sir Roger Carr, chairman of energy giant Centrica, at the time.

"So any system which puts a bid on our prices while our costs are variable presents us with a very difficult business model on which we can invest and make long-term contract commitments and therefore secure supplies to this country."