Berkshire town's first leader (10)
I believe the answer is:
maidenhead
'berkshire town's' is the definition.
(town in Berkshire)
'first leader' is the wordplay.
'first' becomes 'maiden' (as in a maiden voyage).
'leader' becomes 'head' (head is a kind of leader).
'maiden'+'head'='MAIDENHEAD'
(Other definitions for maidenhead that I've seen before include "Place" , "town on the Thames" .)