Old three-halfpenny comic incomplete, one part damaged (9)
I believe the answer is:
dandiprat
'old three-halfpenny' is the definition.
(dandiprat is a historical English coin)
'comic incomplete one part damaged' is the wordplay.
'comic' becomes 'Dandy' (The Dandy was a British comic).
'incomplete' means to remove the last letter.
'one' becomes 'I' (Roman numeral).
'part damaged' becomes 'prat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'dandy' with its final letter taken off is 'dand'.
'dand'+'i'+'prat'='DANDIPRAT'
(Another definition for dandiprat that I've seen is " Insignificant person".)