A Conservative in dirt gives scowl (7)
I believe the answer is:
grimace
'scowl' is the definition.
(I've seen this in another clue)
'a conservative in dirt' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'in' means one lot of letters goes inside another.
'dirt' becomes 'grime' (grime can mean dirt or mud).
'a'+'c'='ac'
'ac' inserted into 'grime' is 'GRIMACE'.
'gives' is the link.
(Other definitions for grimace that I've seen before include "Express wry amusement" , "unpleasant expression" , "Distortion of the face" , "Distorted facial expression" , "Contortion of face expressing pain" .)