National Grid PLC could be ordered to pay tens of millions of pounds in potential fines after electric supply failures caused by the malfunctioning of two of its generators led to transport disruptions and power outages in about a million households, The Sunday Times reported.

Energy watchdog Ofgem asked the U.K.-headquartered utility for an urgent detailed report regarding the power cuts at 5 p.m. London time on Aug. 9. The regulator can fine National Grid as much as 10% of its turnover.

The abrupt power loss caused failsafe measures to cut electricity supply to a part of the network, the newspaper wrote.

National Grid said that the power was restored by 5:40 p.m. London time on the same day.