The Rail Accident Investigation Branch (RAIB) has released its report into the derailment of a Southern Passenger Train in Hooley cutting near Merstham, Surrey on 13 January 2007. The full report into the incident is available here:

A summary of the reports is - On Saturday, 13 January 2007 at 12.23, an eight-car Southern train travelling from Bognor Regis to London Victoria emerged from Merstham tunnel and ran into landslip debris on the track, which derailed its leading wheel-set. The driver saw the debris and applied the emergency brake to slow the train, which stopped after 320 metres. None of the 413 passengers were injured but some needed assistance to reach the public highway. The first coach received substantial damage and some signalling equipment and track bonds required replacement.

The immediate cause of the derailment was that two timber beams from a wall intended to prevent rock and soil spills had been displaced by a six-tonne root ball falling from the cutting side. There were three causal factors and four contributory factors related to the incident. The underlying cause was the lack of guidance in standards regarding root balls, and a backlog of earthworks examinations.