Hostile to piece from Alan Titchmarsh (4)
I believe the answer is:
anti
'hostile to' is the definition.
(anti means hostile to or opposed to)
'piece from alan titchmarsh' is the wordplay.
'piece from' indicates a hidden word.
'ANTI' can be found hidden inside 'alan titchmarsh'.
(Other definitions for anti that I've seen before include "Opposed to followers of Hitler" , "Someone opposed (to a policy?)" , "Opposition member" , "(Person who is) not in favour" , "Hostile" .)