In reply to Lancahsire Bushcraft:
If it's just to hang a tarp/hammock and go for a bivvy then it's the same guidelines as for wild camping in England and Wales - arrive late, leave early, leave no trace and sod off as far from humans and their corridors of travel as you think is reasonable.
A word of warning; wild camping without the permission of the landowner is 'just' trespassing - a civil matter, not necessarily criminal. If you bring knives, axes and other cutting tools into the mix then it could be construed as 'armed trespass' - much more interesting and serious in the eyes of the law.
Depends on many other factors, but worth considering.