Dave Plowman wrote:

nothing legally to stop you doing this in your own house.

or someone else's house, and even charging them for it.

But obviously, if only competent.

of course, it's an existing circuit, not in a "special location" so
part-P doesn't apply.

If it's easy to extend the ring then that could be seen as best, but
spurs are perfectly allowable, make sure the existing socket isn't
already a spur, spurs must be fused if they have more than one single or
double socket.