Every install is different. Are you prepared to dig a trench, or happy with surface wiring?
20mm plastic conduit, with tee boxes below each light may be the best option. 20mm glav would be more robust, but the conduit does age in the weather, and can look a little to industrial.
If you use armour, trenched at the foot of the wall (I assume wall), put a galv trouser box, or a plastic gewiss type box below each light at low level, and run a stab of conduit upto each light. (again plastic or galv).
If using SWA, you would need a 4 core. 1 core for Neutral, 1 core for constant live, 1 core for switched live, and the final core to common the two common terminals of the switch. The armour would be the earth. You would need a seperate run for the sockets.
An idea of what you are fixing to, or even a photo would help.....
Where in Devon??