Leading group in Home Counties of highest status (7)
I believe the answer is:
supreme
'leading' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for supreme that I've seen before include "Best of all" , "Chief" , "Most important" , "Paramount" , "Highest in authority; rich cream sauce (dish)" .)