Andy,The Crabtree metal dolly type is usually O.K.it was always fitted in a good quality cast iron box, with the fixings for the switch interior being taped directly into the cast box giving a good earth. (prviding the conduit was sound). Agree with you on the panel type switch have seen a good number of these shorted and blown up even seen them causing the door of the panel to become live because there has been no bonding strap across the hinge mechanism. Never like to see them on 240v systems. You can get a rubber gasket that fits over the switch dolly but they are seldom fitted.Even that does not make me like them. Company called Arrow used to make lots of them.
