In the sixteen years I've needed a licence, I been checked seventimes, five of which were in the same season all on different venues. 1996 to 1997.
The following two checks both came in the same year (2000) and again on different venues.
All the venues varied form the obvious commercials to quiet day ticket waters. Two of the checks occurred on veryiscolatedclub waters.Both small river stretches that require a walk through two to three fields from the road, where you may only see another angler ever ten visits.
Moral of the story is - nowhere is exempt from checks at any time, however unlikely. Its not worth the risk.