Pretty straight forward once I got the correct tools, originally I didn't have an E18 torx socket.
the main reason for doing this was the occassion grinding and sqeaking noises i was hearing from the near side rear. At first I though it was the pads at fault but when I took the pads off it was obvious the disks had seen better days. Also the pads looked as if they had been recently replaced with cheap items. This also didn't help things as they were a poor fit and didn't have any of the clips/pins etc that the genuine Vaux items have.
So I fitted disks and pads from mr Vauxhall (£70) and cleaned everything up while i was there.
Haven't done many miles on them yet but they brakes feel fine. Definately quieter with no abnormal noises.