Problems on at least one Tube line are set to continue for the rest of the day, after a nightmare rush hour in which seven Tube lines were hit by suspensions or delays.
Nigel Holness the director of network operations at London Underground, apologised to customers, but said problems on the District Line are likely to continue all day.
"I apologise to customers whose journeys on the Tube were disrupted this morning due to a power failure at Aldgate East as well as by signal failures at Barking and Wembley Park," he said.
"Our engineers were on site and worked hard to restore services as soon as possible. The derailment of a South Western Railways service at Wimbledon has also affected the District Line, which remains suspended between Parsons Green and Wimbledon. Our engineers are supporting Network Rail with recovery work, which is likely to continue for the rest of the day."
Commuters were faced with problems on seven lines this morning, including the DLR, Bakerloo, Circle, District, Hammersmith & City, London Overground, and Metropolitan lines.
Meanwhile, rush-hour commuters on overground trains were faced with problems at Waterloo, after South Western Railways said the derailment will cause disruption between Wimbledon and Waterloo until the end of the day.
Just before lunchtime, three lines were hit: