Whip accepting work with Young Conservatives is an imitator (7)
I believe the answer is:
Here is my best explanation:
'an imitator' is the definition.
('copycat' can be a synonym of 'imitator')
'whip accepting work with young conservatives' is the wordplay.
'whip' becomes 'cat' (cat o' nine tails, cat for short is a type of whip).
'accepting' means one lot of letters goes inside another.
'work with' becomes 'op' (common abbreviation for 'opus'. I am not sure about the 'with' bit.).
'young' becomes 'y'.
'conservatives' becomes 'c' (abbreviation in UK politics).
'cat' enclosing 'opyc' is 'COPYCAT'.
'is' acts as a link.
(Other definitions for copycat that I've seen before include "not the original one", "Person imitating another (or cloned pet?)", "Ape", "Mimic", "Some murders are", "Slavish imitator", "One imitating another", "Person imitating others", "Person (or crime) imitating another" and "Plagiarist possibly".)