A light-hearted pair of Conservatives, very casual (11)
I believe the answer is:
perfunctory
'very casual' is the definition.
(perfunctory can mean casual or lacking interest)
'a light-hearted pair of conservatives' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is located in the answer.
'of' could be 'o' and 'o' is found within the answer.
'conservatives' could be 'c' (abbreviation in UK politics) and 'c' is located in the answer.
'light-hearted' could be 'fun' (light-hearted means fun or unserious) and 'fun' is present in the answer.
The remaining letters 'try' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for perfunctory that I've seen before include "Done as a formality only" , "Done with little effort" , "Not thorough" , "Careless or cursory" , "Hasty and superficial" .)