Well, much as I like the riding that I have around here (the Isle of Man) I think that for trails to fit the "awesome" description you have to have mountains, and half decent ones at that. Places where you could easily get lost, die and never be found....
So in Britain that only really leaves you with the Scottish Highlands.
I have proper mountains in Greece too (well, up to 2,400 metres) - my wife hates me going up into them on my own, as I can be gone all day and there's usually no phone coverage.