Exclusive: Iran shut down a British power plant for four days in an unprecedented cyber attack, @Telegraph can reveal tonight. It is thought to be the first time that hackers affiliated to the Iranian regime have succeeded in closing down such a facility in the UK, and believed to be the most successful cyber attack of its kind. The incident took place at the same time as a series of attacks on US water infrastructure that affected 12 states last month. The British attack was on a small electricity producer and had no adverse effect on national power generation or supply. But it demonstrates the power of Iranian hackers to infiltrate and shut down national infrastructure. In response, the Government has briefed energy CEOs on how to keep their facilities safe. Story w/@RozinaSabur and @mattotele