More detail
From from the book on trials aircraft crashes (forget name - I only have a copy of relevant page)
8 Jun 51. Wyvern 2. VW869. Lt Cdr DK Hanson (Graduate No.9 Course) - C Sqn A&AEE. Airtest following prop change. Canopy imploded and the rails detached in flight and hit the fin causing structural failure of the empennage. The violent yaw which ensued created a gyroscopic couple on the contra-rotating propellors resulting in the blades meshing and breaking up which then caused the engine to detach from the airframe and the subsequent disintegration of the aircraft. The pilot operated the ML ejector seat but was rendered unconcious when his leg caught on the control column during the ejection sequence. Pilot thus unable to operate the manually sequenced seat and was killed on ground contact. All Wyverns grounded until an ejector seat with a greater degree of safety installed.