Well the 1974 act was a good start, as up to that time the safety of employees wasn't a particular concern of employers as my dad found out one day when he went to adjust the height of a circular saw blade, and discovered the hard way that it didn't have the expected guard blade protecting its underside.
He said afterwards that he didn't feel a thing at the moment it happened it was the shock of seeing four fingers missing that caused him to keel over.....
Humm.... Well the earth had come off at the distribution board and the whole house was wired with this lead sheathed cable. So presuming that the lead sheathing was all bonded together then there would have been quite a lot of Capactive leakage from the live to earth, as one could assume that at some stage the un-earthed lead casing would be connected to another earth in the house, via lets say something like an immersion heater or similar appliance, so I reckon that their would have been sufficient Capactive and an unknown amount of resistive leakage sufficient to trip the RCD.
There was quite enough current there to prevent me from doing anything about it, and FWIW I have very dry skin and my hands were very dry on that day, so I reckon that a trip would have been taken out.