So at long last I have an offer on the house
The sales information form ask who owns the boundaries, and to be honest - I don't rightly know - it's a modern house and none of the fences have been an issue so far.
2/3 fences are onto public land so I guess they're mine. If I'd had any issue with the other fence I'd have just knocked on next door and asked. We have the nice side of that fence - if that helps