Best of luck with it macphil. I had an RT Alize Megane too
I saw a Megane earlier tonight where its indicators didn't work, instead the brake light and centre brake light flashed alternately! That is advanced earthing failure I think.
It is a simple job to relocate the earth, just make sure you attach your new earth to the correct part of the wiring board in the clusters. It is really obvious if you follow the track around to the plug connector
The earth point you choose on the car is up to you, but using the existing earth points will do fine, just make sure they are nice and clean and the contact is good