Ofgem’s investigation will also be looking at whether energy companies “made the right decisions both in the numbers of customers disconnected and whether those customers disconnected were the right ones”.Keith Bell, professor of electrical engineering at the University of Strathclyde, said the report questions whether Network Rail has sufficient safeguards in the event of a power cut.“The event shows the need for and value of system defence measures. However, because it cannot be guaranteed never to trigger them, they need to be implemented in a cost-effective way that minimises the impact on critical supplies.“Operators of those critical supplies should take steps to ensure sufficient resilience.”Professor Dieter Helm, a government adviser on the country’s energy policy, wrote online how “something fundamental has gone wrong” when a lightning strike can cause a power cut “that should never have happened in the first place”. Explaining how key infrastructure needs a reliable supply of electricity, he said new equipment is needed to improve energy “security” on a network which is becoming “fragile” because it is relying on more “intermittent renewable energy”.However, investment in huge batteries to store power and more cabling to transport energy from remote wind farms is likely to see an increase in consumers’ energy bills. A major power cut caused by a single lightning strike saw more than 1 million people lose power, and nearly 1,500 trains cancelled or delayed, a report reveals.The bolt of lightning triggered an off-shore wind farm and a gas power station more than 100 miles apart to “independently” go off grid in what were “almost simultaneous unexpected power losses”.An interim report by National Grid into the causes of the power cut on Friday August 9, found the lightning strike hit the network at 4.52pm. Within minutes Hornsea off-shore wind farm and Little Barford gas power station suffered a failure, but National Grid did not have sufficient levels of “backup” power to cope with the loss in supply from those generators.Consequently, the system automatically disconnected customers on the distribution network, with about 5 per cent of electricity demand being turned off to protect the remaining 95 per cent.That day 30 per cent of the country’s energy was coming from wind power, a further 30 per cent from gas and 20 per cent from nuclear power, with the rest from other sources, the report adds. Energy experts and critics of the UK’s increasing reliance on renewable energy are warning that new infrastructure, including battery systems to store power to cope in the event of an outage, is now desperately needed, raising the prospect of soaring energy bills. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Commuters were stranded by the power cutCredit:Lewis Pennock /PA Ofgem, the energy regulator, responded to the report by launching an investigation into whether National Grid should have held enough reserve supplies of electricity to cope.The 26-page document also reveals how a series of local “embedded generators”, often small renewable power plants and diesel energy farms, may also have been shut down by the lightning which hit a transmission circuit. These generators are not controlled by National Grid as they feed into local rather than national power networks. The lightning strike was one of many to hit the grid that day with strikes “routinely managed as part of normal system operations”.The report explains how 1.1 million customers lost power for between 15 and 50 minutes.Thousands of rail passengers had their journeys severely disrupted. In total, 371 trains were cancelled, 220 partially cancelled and 873 services delayed. London St Pancras and Kings Cross stations were temporarily closed due to overcrowding.Some 60 trains operated by Govia Thameslink Railway (GTR) in the South East “reacted unexpectedly to the electrical disturbance” – half of which needed an engineer to be sent out to reset the train. The issues will be investigated by Network Rail and GTR.The outage also stopped traffic lights from working, plunged Newcastle Airport into darkness, and affected Ipswich Hospital. Ofgem has the power to fine companies at fault up to 10 per cent of their UK turnover.