The Rail Accident Investigation Branch (RAIB) has released its report into the derailment of a London Underground Central Line train near Mile End station on 5 July 2007.
The full report into the incident is available here:

A summary of the key points from the report are - On Thursday 5 July 2007 a westbound Central line train struck a roll of fire-resistant material which was lying on the track between Mile End and Bethnal Green stations. The first three bogies of the train were derailed and the driver applied the emergency brake, stopping the train after 148m. There were no serious injuries caused by the derailment, but 20 passengers received medical treatment. All 520 passengers were evacuated from the train along the tunnel to Mile End station. The derailment also caused some damage to the first two carriages of the train, to the track and to one signal.

The immediate cause of the incident was a roll of fire-resistant blanket, approximately 1.8m long, lying across one rail. The blanket had been stored in a passage the previous night and weighted down, but the wind from passing trains had caused it to unfurl and fall onto the line. There were four causal factors and four contributory factors related to the incident. The underlying cause was the lack of a comprehensive risk analysis being performed to support the use of fire-resistant blankets.