Hi Daz
I have been looking around for the same type of letter that you are asking about, see below and attached file to see what i have decieded to use hope this is of some help to you.
AUTHORITY TO SHOOT
I ………………………………………….. Of …………………………………………..
In my capacity as, Landowner, Tenant, Estate Manager, Game Keeper
Address
…………………………………………………………………
…………………………………………………………………………….
………
