The british BC's blew up mainly due to piss poor ammo control procedures, including the removal of safety doors between the magazine and turret and the storing of extra cordite charges in the turrets. Also the British propellant exploded, the german one burned.
A contributing factor was the RN's emphasis on rate of fire as it believed the best way to fight an opponent was to shower it with as many shells as possible. In order to keep up the rate of fire gunnery crews left the flashlight doors open with disastrous consequences.