County Durham's top store wrecked (6)
I believe the answer is:
dorset
'county' is the definition.
(I've seen this before)
'durham's top store wrecked' is the wordplay.
'top' indicates taking the first letters.
'wrecked' indicates anagramming the letters.
The first letter of 'durhams' is 'd'.
'store' with letters rearranged gives 'orset'.
'd'+'orset'='DORSET'
(Other definitions for dorset that I've seen before include "part of England" , "Strode around English county" , "A SW county" , "County of south-west England" , "English county -- sorted (anag)" .)