Not a fan of conservationists visiting capital (4)
I believe the answer is:
anti
'not a fan of' is the definition.
(I've seen this in another clue)
'conservationists visiting capital' is the wordplay.
'conservationists' becomes 'NT' (National Trust).
'visiting' is an insertion indicator.
'capital' becomes 'AI' (resembles 'A1', old-fashioned term for excellent).
'nt' put inside 'ai' is 'ANTI'.
(Other definitions for anti that I've seen before include "An opponent - opposed to party policy, etc" , "Definitely not pro" , "Prefix meaning against" , "Adversary" , "on the other side" .)