If the cable from the socket before the fuse is 1mm² then this is power wiring and the minimum size is now 1.5mm², but really it will not be a problem and could be considered as the spur is for lighting only, perhaps.
Thanks, hadn't thought of that. Think I'm going to C3 it anyway. I know in reality it's never going to be a problem but it just seems like a bit of a bodge.