There is no checker
To create one there is one problem from the checker "By counties I mean the county names: Leicestershire, Berkshire and Lancashire for example. NOT the geocaching.com counties such as Northeast England and Northwest England"
Thatmeans that the the information is not precaclulated by pgc and polygons of the counties have to be added to the checker. It is posibel to do that if somone priovides the polygons
the GenericPolyChecker can probibly be used if correct plygons are proovided. the might be a problem if the border polygons have to many points and the script will timeout