Hey, thanks for replying, everyone.. OK so:
Trailer access: Yes, there's trailer access so of course I could lead them to it once they've learned to feed from a bag. Duh.
How will you fence it? It's already fenced down the one side of the boundary - if it's something I end up being really keen to do I'd fence an area off for them. I wouldn't have thought I'd keep more than 3 or 4 pigs. Roughly how much space would they need?
Do you have level ground for a pig ark? Yes - there are some plateaus which could work for an ark.
Does it have a permanent water supply? A steam runs alongside the boundary but not sure if that's suitable unless I rigged up a way to divert some water to allow them to wallow. For drinking water I think I'd be able to put in a trough along the boundary.
When do you plan to raise them - bear in mind Winter conditions in N Wales: Presumably I'd raise them over Spring/Summer?
Verdifish - I saw kune kunes when I was researching but I guess I discounted them due to the fact that they were kiwi pigs and not native to the UK - I love the idea of the electric fencing as well, if it works - I'll certainly get in touch for advice if I get that far! The woodland has a lot of bramble and stinging nettle in it at the moment - presumably I'd need to clear that?