why not underground ?

The cost of poles properly seated + cable etc would possibly be more expensive than a trench.

From memory 

- 6mm2 TPS cable, UV rated, supported by a catinary wire. 
- 3 metres above ground, or 4.5m if vehicles are capable of being driven through the area under it.

If its a short distance I'd probably also suggest putting it inside some 25mm solar duct 

Edit: Its outside the homeowners legal abilities so you need to work under supervision which means calling out an electrician, them telling you what to do, then when you have installed it, they come back and connect it up. They then issue you a compliance certificate.

Thanks for the info.

It will be a permanant eyesore if you go overground. Get the ditch dug and while you are throwing stuff in it for power, put some conduit out there for future fiber run to the place.

rhy7s: The route is through difficult terrain and vegetation, though not long, 30m or so.

So how do you walk there at the moment?  You could trench the same route?

Aredwood: 

If you only need the power for some lights. Might be far easier just to rig up your own cable and just run 24V over it for some LED lights.

Or if only lights look at a solar panel to charge a battery.

Mind the lightning strike protection!