The accident occurred in 21:17 last Friday, when the last carriage was derailed at low speed, shortly after the train left Hammersmith travelling eastbound to Barons Court. Passengers described hearing "a big bang" and seeing smoke filling the carriage and sparks as the rear of the Piccadilly Line train came off the tracks. Passengers were rescued from the tunnel by emergency services and underground staff.

There were no reported injuries to the 76 passengers on the Piccadilly line train. London Underground launched a full investigation. "At this early stage in the investigation, it appears that a broken rail was the cause of the incident. Overnight, engineers worked to replace the broken rail and it has been removed for further tests. The Piccadilly line train was also removed overnight to a depot for tests", says London Underground statement.

The BBC said rail staff at the scene had blamed the derailment on a broken rail. It's rusty appearance suggested it had been cracked for some time, it was reported. Passenger Samantha Ceranka told the press: "We just heard this big bang and the train crunched as it stopped. Sparks lit up the whole carriage, the lights went out for a bit and there is loads of smoke everywhere. It was very scary. People started to panic a bit. All of us wanted to get out of there. Some people were trying to open the emergency exit but it didn't work."

The Rail Maritime and Transport Union says it wants to know how often the tracks involved in the Piccadilly Line Tube derailment were inspected.

Lynne Featherstone, London Assembly Transport Committee chairman, said the Assembly would be holding an inquiry into the accident. She added: "The London Assembly will be making a full inquiry into what has happened. Our investigation into the Chancery Lane derailment is that it was an accident waiting to happen; I hope that has not happened this time around."

Earlier this year the Central Line was closed for three months following a derailment at Chancery Lane station in January. A report into the incident, which left 32 people injured, found it was caused by gearbox failure. The investigation's chairman, Dr Roger Aylward, said the accident should have been prevented and made 24 recommendations so Tube bosses could "address the deficiencies identified."

TfL Web page