Is it me or is the solution fairly obvious here.
assuming the socket is not already a spur!!
Fit a FCU next to the socket, fuse down at 5A, 1.5mm up the wall from FCU to switch to Light fitting!!!
Please read the thread:
Is this the feed for the upstairs lighting circuit?
yes.
This is the FEED from the consumer unit to the upstairs lighting circuits.
An FCU is not a proper way of providing this.