If you want lots of real wilderness as opposed to just farmland you should go to Scotland.
Do this
http://www.west-highland-way.co.uk/home.aspand then this
http://www.greatglenway.com/The_route.htmYou can go off the trail as you wish, and there are designated areas to camp along the route.
This route will include Ben Nevis, the tallest mountain in the British Isles, and Loch Ness.