From reading your post here Stuart, it does appears you do pest control and therefore, a degree of shooting, for a living Stuart. That's good.
A farmer generally expects that you will be simply wanting to go shoot and hunt on his land, in exchange for culling the pests that blight his business. Thus, he gives you and me and the other lads here permission to do so. Seems you have offered him favours in unpaid skilled labour, above and beyond anyone else's reasonable expectation, to secure shooting rights here mate?!
That's probably why he's wondering, you see old lad!
Simon
F