Major power failures have been reported across large areas of the UK, affecting homes and transport networks.
National Grid said it was caused by issues with two power generators but the problem was now resolved.
Blackouts were reported across the South East, Midlands, South West, North East and Wales.
Trains were delayed and cancelled across England and Wales, and the drop in power affected traffic lights in London.
At the height of the Friday rush hour, all trains out of King’s Cross were suspended.
The BBC’s Emma Petrie said there was a Tannoy announcement asking passengers to leave the station.
Boards at Waterloo station showed no trains departing on any platforms.