Hi all
Not a grey area at all, its quite simple, if you think your shot will land on permanent wetland (ditch, burn, marsh, estuary), then you cant use lead shot. Technically you can stand at the edge of the saltmarsh/estuary and fire landward at your quarry and be within the law.
However, in managed wildfowling permit zones there is additional rules that come with rights of access for shooting, one of these is often that you do not even carry lead shot.
There is a great BASC leaflet about it that I think you can download from there website.
A simple rule of thumb is, small in