HUNDREDS of thousands of homes across the UK came within hours of power cuts after the National Grid issued an emergency call for electricity companies to reduce demand on one of the coldest days of the year.

The companies were preparing to cut power or dim the lights on Thursday by lowering the voltage, after the grid issued a warning of a possible problem between 4.30pm and 6.30pm. Power generators were told to make more power available on the system, while distribution companies were informed that if no more power were made available they might have to cut some customers off temporarily. The highly unusual shortage comes as fears mount over the security of Britain’s energy supplies. There was also concern that there was insufficient capacity, even though most industry was still on a Christmas break.

Power cuts to households are supposed to be a last resort and the National Grid said this year that even in an extremely cold winter they could be avoided. Big energy users in industry are supposed to be cut off first in the event of a power crisis. The first warning that the grid’s safety margin was depleted came early Thursday morning, but by breakfast time the warning had been increased to a high risk of demand reduction order. The order was cancelled at 6pm on Thursday when it became clear that demand would not be as high as feared.

About 40 per cent of Britain’s power stations will be due for retirement in the next 15 years, as all but one of the nuclear power stations are decommissioned and older coal-fired power stations are closed because of new European Union directives on pollution. Britain has also become a net importer of gas, because North Sea supplies have been running out more quickly than expected.

Gas supplies are extremely tight this winter and will be next winter, as the new storage facilities and pipelines are built to facilitate this transition.

The amount of electricity available this week has been lower than usual after some power generators temporarily shut down their gas-fired power stations because of the high price of gas. Wholesale gas prices have been 50 per cent higher than last winter.

Last month, the Prime Minister announced an energy review, which is expected to report in June. However, industry has said that the Government’s last energy White Paper, only two years ago, ignored the challenges that were already becoming clear.

The emergency warnings on Thursday occurred because the safety margin of available electricity was about a third lower than it should be. The shortfall fluctuated between 1,300 and 1,700 megawatts, between a third and a half of a typical safety cushion. The grid needs a comfort zone of between 2,000 and 4,000 megawatts available above peak demand. On Wednesday and Thursday it issued an NISM — notification of inadequate system margin — calling for 1,300 to 1,700 megawatts more, enough for up to 1.7 million homes.

“The NISM demonstrates that the system is working. This is a standard tool for us. The warnings are just the control centre doing their job,” a spokesman for National Grid said. Between 8 and 10 NISMs are issued a year, but only about one a year becomes a high risk of demand reduction order. The last such order was in December last year.

Power industry sources said that they came very close to cutting about 220,000 homes off for a couple of hours on Thursday afternoon or lowering the voltage to all their customers by 3 per cent. This would dim the lights slightly, but would not generally be noticed by most homeowners.

A spokesman for Ofgem, which regulates the gas and electricity markets, denied that the warning showed that the energy network was fragile. “There was always a margin of about a gigawatt — enough for a million homes. This is a tool that National Grid uses to send a signal to the market to increase the available supply.”

Explore UK News

• Crime News

• Education News

• Health News

• Science News

• Scotland News

Times Recommends

• Tree stump 'shows image of Virgin Mary'
• BBC drops Strictly judge for younger model
• Trafalgar Square 'reduced to a spectacle'