Outside Socket

No that is not correct. You may use any kind of cable anywhere as long as it is suitably mechanically protected from any likely damage. You can run SWA on a fence line but because fences tend to blow away sometimes this may not be the best method. Having said that I have no difficulty with SWA fixed to fences which are in reasonable condition, and it is quite safe. You need to have 30mA RCD protection, best inside the house, and an IP67 enclosure for example the MK ones. Be aware that the appliances you use also need weather protection!

Great! The SWA will be spurred from the house ring with 30mA RCD protection at the CU.

SWA with feed IP67 enclosure with a socket and feed to IP67 led deck lights.

SWA will be clipped to concrete posts/gravel boards.

Often, it is not always financially viable to bury cables owing to uncertain ground conditions and installed overhead because there is no definite support posts to cantilever the catenary. Another obsticle might be if the house is not owned by you then permission will need to be sort.

How stable is the fence? If its supported with concrete pillars then I see no reason why the cable shouldn't use the pillars to support the SWA.

The height of installation is dependant on what is likely to run underneath. So in the case you are suggesting that it will have to run over a walk way.

IMO, if you, or your family are the only ones who'll have access and it doesn't go across a road then perhaps common sense may provail.

Legh

Just as an aside. I recommend you consider fitting a DP switch at the point of spurring within the house. Just helps mitigate against your new external socket being damaged/letting water therefore it can quickly be disconnected to avoid nuisance tripping of RCD until subsequent repair/replacement can be made.

I might be slightly wary of drilling into concrete fence posts. As they'll likely have steel reinforcement, which will rely on a certain cover of concrete to protect the steel from the elements and prevent corrosion, drilling is likely to allow rainwater to penetrate much closer to the rebar, allowing corrosion which may quite quickly cause the concrete to spall and so the the post to fail. Let alone the difficulties if you hit the rebar itself when drilling or general weakening of the concrete itself by making holes in a structure that was intended to be solid.

   - Andy.