Blackouts in New York sparked concerns for UK power supplies

The news comes amid a backdrop of high profile power cuts around the world which had prompted fears the UK could be facing a black Christmas.

Ofgem said: "We are confident about a normal winter and even in exceptional circumstances consumers should not be concerned but we do not want to give a 100% guarantee."

The power regulator added that it would monitor the market closely, warning "there can never be any room for complacency when it comes to keeping the lights on".

In a report to Ofgem, National Grid said the recent restart of a couple of mothballed power stations has helped raise the safety cushion of reserve power available at peak demand to 17.7% in October from 16.5% in July.

This safety margin was once as high as 20%.

Experts have said they do not fear a shortage over Christmas, as businesses are closed.

However, the grid faces most pressure in January when offices and factories return to work after the festive holidays.

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But chief executive of the Association of Electricity Producers David Porter says prices need to increase further to give firms the incentive to power up mothballed plants.

"If wholesale prices in the electricity market rise sufficiently then companies will restore power stations that have been mothballed and we'll have them available to meet our winter demand.

"So far price rises have been limited, albeit recently they have begun to creep up and there are signs that companies will bring back power stations."

Following a slump in power prices, prompted by deregulation and increased competition, power companies have mothballed 4,600 megawatts of capacity - the equivalent of 7.1% of the current generating capacity in England and Wales, Ofgem said.