From the UK RAIB web site:

The RAIB is carrying out an investigation into the derailment of a freight train just north of Shrewsbury station.

At 14:13 hrs on 7 July 2012 all wheels of the leading bogie on the 16th wagon of freight train 6M61 derailed as it travelled from the Down Main line to the Down Main Crewe line over a set of facing points. The train was travelling at 14 mph and comprised a locomotive and 19 wagons carrying coal from Portbury Dock to Fiddlers Ferry. The train travelled approximately 80 metres in the derailed condition before coming to a stand. The driver of the locomotive was uninjured and the wagon remained upright. However, there was significant damage to the track, points and crossings.

 Cms Resources Shrewsbury

Image of the derailed wagon

The RAIB’s preliminary investigation has discounted both the manner in which the train was driven and the operation of the signalling as factors in the derailment.

Early indications are that the points involved in the derailment were correctly set and locked. However, marks on the rail indicated that a set of wheels on the leading bogie climbed the left-hand switch rail, which was showing signs of damage and wear. The RAIB’s investigation will seek to understand the mechanism that resulted in the train derailing. This will consider the condition of the track, including the points that were involved, and the wagon.

The RAIB’s investigation is independent of any investigations by the safety authority (the Office of Railway Regulation) or the British Transport Police (BTP).

The RAIB will publish a report, including any recommendations to improve safety, at the conclusion of its investigation. This report will be available on the RAIB website.