A Conservative nobleman's narrative (7)
I believe the answer is:
account
'narrative' is the definition.
(I've seen this in another clue)
'a conservative nobleman's' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'nobleman' becomes 'count' (count is a kind of nobleman).
'a'+'c'+'count'='ACCOUNT'
(Other definitions for account that I've seen before include "Bill; importance" , "Statement of transactions and costs" , "Bill - story" , "Report of an event" , "Explanation of conduct" .)