This is often done by using a Fused Connection Unit (fused spur), either next to the socket (unswitched type) and run in 1.5mm or run direct from socket in 2.5mm to a switched FCU using switch to control light wired from FCU in 1.5mm, commonly done for add on conservatories etc.
In either case fit a 3A fuse,
your switched fused connector should also be of the RCD type if you intend to bury the cable in the wall and the circuit isn't already RCD protected. Also you should be aware of the regs for doing this in any 'special locations'
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