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Thanks for all replies, newkid I'm still alive and can assure you I'm competent enough to do a bit of domestic wiring.
So the final answer is gang refers to the number of switchs or sockets on the plate, as mac309 states ie a double socket is a 2 gang socket, a single socket is 1 gang, the same applies with switches.
Woodpam, a switch that controls a light from 2 positions is a 2way switch. This has 3 connections points on the back for the wiring, a simple 1 way switch has 2 connection points.