Big success in a Whitehall farce (3)
I believe the answer is:
hit
'big success' is the definition.
(I've seen this in another clue)
'in a whitehall farce' is the wordplay.
'in' says the answer is hidden in the clue.
'HIT' is hidden in the letters of 'whitehall farce'.
(Other definitions for hit that I've seen before include "Best-selling record" , "Knock" , "Badly affected" , "not to miss!" , "that pleases the public" .)