National Grid has had to call on Britain’s struggling power stations to increase output for the fourth time this month as spot gas prices soared to 62p a therm a level not seen since March 2006 and a jump of about 40 per cent on prices last month. National Grid asked generators three times yesterday alone to supply more power and put them on notice to provide an additional 1,900 megawatts enough to power 1.9 million homes for today, as cold weather sweeps the country. The warnings came because the safety margin of available electricity was about a third lower than it should be. The grid needs a comfort zone of between 2,000MW and 4,000MW available above peak demand. The notification of inadequate system margin (NISM) is calling for 1,300MW to 1,700MW more. Usually between eight and ten NISMs are issued each year, but sources in the electricity market have noted that there have been four since last month, despite the weather being reasonably warm. The problems have been exacerbated because three of the country’s eight nuclear reactors, which provide a fifth of the UK’s electricity, have been shut down. A spokesman for National Grid said that there was no cause for alarm. “This is one of the tools we use to get information to the market, to make sure that enough capacity is available,” he said. A spokesman for Ofgem said that this was a normal procedure to encourage more generating capacity back on-line. “We have a comfortable safety margin this winter of around 20 per cent,” he said. Concerns over capacity have led to spikes in the gas price recently and industrial users are bracing themselves for a difficult winter. Retail consumers also learnt yesterday that there was little chance of price cuts as suppliers are wary of high forward prices for the coming months.