I would say that if you were walking your dog on a lead on the public road you stand a reasonable chance of 'No further action'.
If any of the following aggravating factors apply I would say that you stand a reasonable chance of receiving a summons:
-Having been seen to run your dog on the farmland or shine your adapted torch over it.
-Carrying any further 'equipment' (knife, bag, red lens etc.)
-Having previously come to notice for a similar incident
-Any dead hares/rabbits having been found nearby.