Policeman needs to make impression in court work (9)

'policeman' is the definition.
(informal term for a policeman)

'to make impression in court work' is the wordplay.
'to make impression' becomes 'dent'.
'in' means one lot of letters goes inside another.
'court' becomes 'woo' (synonyms).
'work' becomes 'op' (abbreviation for opus).
'woo'+'op'='wooop'
'dent' placed inside 'wooop' is 'WOODENTOP'.

'needs' is the link.