National Grid (NG.) had evidence that the shift to renewable energy was putting Britain’s electricity supply at risk months before the biggest blackout in a decade, The Mail on Sunday can reveal. The company, which is responsible for keeping the lights on, has downplayed the role of wind energy in the power cut that caused widespread chaos earlier this month. John Pettigrew, chief executive, described the outage as a ‘once-in-30-years’ event and said there was ‘nothing to indicate there is anything to do with the fact that we are moving to more wind or more solar’. Yet in April, National Grid published research warning that using more renewable power sources posed a threat to the network’s ‘stability’. In a report based on a £6.8 million research project, National Grid admitted that renewables increased the ‘unpredictability and volatility’ of the power supply which ‘could lead to faults on the electricity network’. -The revelations come as energy regulator Ofgem and the Government continue to investigate the causes of the blackout.