South Western Railway train derailed on 'unsafe' tracks
A train derailed in Wimbledon after a stretch of track was "not inspected or maintained for many years", a report has found.
Four people were injured when a South Western Railway train came off "unsafe" tracks on 6 November.
The Rail Accident Investigation Branch (RAIB) said there was confusion between London Underground and Network Rail as to who was responsible.
It said both firms were unable to explain why patrol diagrams varied.
The report added that Network Rail and London Underground could not explain why these diagrams "did not match the location agreed between the two organisations in 1994".
"The consequence of this oversight was that the track was not being inspected or maintained for many years and so degraded into an unsafe condition."
A spokesman for Network Rail said: "It's not clear how the discrepancy between the two boundaries first came about, but we can assure our passengers this has now been resolved."
London Underground has been approached for a comment.