Laying electric cable maybe years in advance

I would recommend you lay Steel Wired Armoured (SWA) cable. The 17th wiring regulations say "522.8.10 - Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, cable buried in the ground shall incorporate an earthed armour or metal sheath or both, suitable for use as a protective conductor. The location of buried cables shall be marked by cable covers or a suitable marker tape. Buried conduits and ducts should be suitably identified. Buried cables, conduits and ducts shall be at sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground.". 'Sufficient depth' is a bit of a loose end, the agricultural standard is 60cm so you wouldn't be wrong if you went that deep. Get your local electrician to visit and suggest the correct cable cross sectional area for your project. I hope that helps

The short answer is yes, get an electrician in to advise you on possible routes, expected loading, a few calculations for size of cable, he could then terminate the cable both ends test it and issue you with a suitable certificate. Also this would be notifiable to building control.

How about laying in suitably sized conduit fitted with a rope 'pull-through'? That way you can fit the cable at the same time as the building work.