BASC have drafted a template for permission for members undertaking pest control, or other shooting.  This form can be used where no money is changing hands. It is equally applicable for deer control as it is for rabbit and woodpigeon control.
 
This is NOT intended to be compulsory, but simply to help members. Its value is that you can immediately show that you have permission to be on the land with your firearm to control pests.

  Shooting permission slip