call 999 yes I would the second I clocked a firearm and someone 'poaching' but is it that easy? Who's to say that once the police arrive and the guy was actually a deliberate poacher?, who's to say that when the landowner finds out he won't hit the barn roof and tell you to f'off cause his lands now going to get trashed? The 'right' thing might create more trouble than it's worth and see the loss of a stalking ground if played wrong.
It's easy to play the moral responsibility card but that's not our card to play in this one, we weren't there and it wasn't our call.
He did ask for opinions...