Brilliant guys, thanks for your help. Especially you terrymac for sticking with me all the way through! One final thought, I'm going to need to put some polyfilla in the hole in the wall once I've finished the job. Is that likely to cause any problems as it will be in contact with the terminals and the wires (there isn't enough space behind the wall to push the terminal all the way back through)
Will the light fittings base plate not cover ,or accommodate the terminal block ? Does it really matter if there is a hole behind the baseplate ? Bear in mind we have no idea what the light fitting / base plate looks like !!
No that's a fair question, but in short as the old & the new fittings are different shape/sizes, it was impossible to fix the base plate over the existing hole as the screws would be in a hole (!) so I've had to drop it an inch & aiming to fill the hole in without damaging the wires/lights
Nice job ,and the switch you chose is incredible ,blends in so well you can't even tell it's there !!!!!!!