Further to BOAC's input, it was thought that the cockpit Wander Lamp had become dislodged from it's mount and had found it's way under the seat. As the seat was motored to the fully 'down' position, to get the pilot's eyes out of the line of the setting sun, the lamp triggered the mechanism for manually(?) firing the drogue chute, dragging the pilot out through the canopy and unfortunately shredding the main chute in the process...
-RP