Conservative, trendier and cheerful (7)
I believe the answer is:
chipper
'cheerful' is the definition.
(similar in meaning)
'conservative trendier' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'trendier' becomes 'hipper' (hip can mean trendy or fashionable).
'c'+'hipper'='CHIPPER'
'and' acts as a link.
(Other definitions for chipper that I've seen before include "Debonair" , "type involved in 6 [CARPENTERING] ?" , "Smart" , "full of beans" , "Happy" .)