The safety cushion is the spare generating capacity that is available to cover events such as unplanned power plant failures or sudden spikes in demand, for instance when popular television programmes are showing.

In summer last year the safety cushion, or margin, fell to 16 per cent of the total capacity of 67 gigawatts. The level, described by industry experts and unions as dangerously low, was far lower than the margin allowed before privatisation of the industry.

However, as forward prices for electricity rose last winter, generating firms brought their mothballed plants back into action, and the margin rose to 21 per cent in December last year.

Ofgem, the gas and electricity regulator, has tried to boost the safety cushion this winter by allowing generators that only want to run plants for the season to pay lower electricity transmission charges.

Generating firms have already been positioning themselves for the cold months, with companies, including Centrica and ScottishPower, buying power stations. Another two new gas fired power stations, supplying 2.3 gigawatts of power, are being built, along with 186 megawatts of wind power.

Centrica exercised an option to buy Wainstones Power, a subsidiary of Carlton Power, in August. The purchase gave the UK’s biggest energy supplier an option to develop a new large scale power station in Langage, Devon.

Ofgem officials said yesterday that the regulator would watch to see if the industry responded correctly to price signals by building new plants.

“If this does not happen, then Ofgem would want to understand why and consider any action that may be required,” the watchdog said in a statement.

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