A harsh winter could plunge the country into darkness, according to the National Grid.
EU legislation has forced older polluting coal and oil power plants to be turned off, which has reduced availability by 20% since last winter.
This has led to the UK’s electricity safety margin plunging to 5%, half of last year’s figure and the lowest since 2007.
The margin is calculated as the difference between peak demand and available supply, with the reduction of coal-fired power plants cited as a major factor.
National Grid made the glum forecast in its Winter Outlook Report 2013/14, admitting that the margin was “tighter than we have seen historically”, while adding there was enough to meet the country’s needs.
But power rationing remains a possibility if a severe winter increases demand, according to industry regulator Ofgem.
It says that risks to the security of electricity supplies are now increasing at a faster rate than previously expected, having previously warned that there could be energy shortages by the middle of the decade.
National Grid operations manager Chris Train said its latest report took into account a range of data based on experience, historical information and feedback from the market.
“While there have been power station closures since last winter, the information suggests that the market can meet demand in cold weather.
“But as the system operator, we’re never complacent and it’s up to us to be ready to balance the system in real time.
“We believe we are ready and have the tools we need to play our part,” he added. Angela Knight, chief executive of Energy UK, which represents energy companies, said: “National Grid has demonstrated that the UK’s demand for energy is getting closer to the amount we can produce or buy in.
“We have enough energy now but this timely report shows that, as Energy UK has been saying, investment is urgently needed to ensure we build the new power stations we are going to need.” Scotland ground to a halt in the early 70s as industrial action by miners led to regular power cuts and three-day weeks for workplaces and schools.