Chris Green wrote:

Is there actually stuff in BS7671 about caravan wiring?

From 17th ed (as I don't have 18th ed)

721.421.2

The wiring systems shall be installed using one or more of the following:

(i) Insulated single-core cables, with flexible class 5 conductors, in
non-metallic conduit.

(ii) Insulated single-core cables, with stranded class 2 conductors
(minimum of 7 strands), in non-metallic conduit.

(iii) Sheathed flexible cables.