Many thanks to all for the electrical advice on other threads. I am
aware of Part P - I am trying to get various things sorted out and
cables put in before getting an electrician in to do the final stages.

Having thought a bit more about my garden wiring I would like to be
able to control separately both a small fountain and some outdoor
lighting from within the kitchen. I would take these off the same 13A
spur from the ring - the load would be no more than 300W.

Rather than running two cables can I (for the sake of neatness and
economy of cable) use four-core cable, with two separately-switched
lives? The fountain and the lighting would then both share the neutral
and the earth. Just need to know so that I can order some cable and put
it in now.