Alan Titchmarsh's a bit contrary (4)
I believe the answer is:
anti
'contrary' is the definition.
(I've seen this in another clue)
'alan titchmarsh's a bit' is the wordplay.
'a bit' says the answer is hidden in the clue (the answer is formed by a bit of the clue).
'ANTI' is hidden within 'alan titchmarsh'.
(Other definitions for anti that I've seen before include "Who pooh-poohs all" , "Opposed to followers of Hitler" , "Definitely not pro" , "Hostile" , "[NO MAN]" .)