Smart to celebrate with Conservative on way back (6)
I believe the answer is:
clever
'smart' is the definition.
(similar in meaning)
'celebrate with conservative on way back' is the wordplay.
'celebrate' becomes 'revel' (reveling is a kind of celebrating).
'with' is a charade indicator (letters next to each other).
'conservative' becomes 'C' (UK political abbreviation).
'on way back' says the letters should be written in reverse.
'revel'+'c'='revelc'
'revelc' reversed gives 'CLEVER'.
'to' acts as a link.
(Other definitions for clever that I've seen before include "Gifted" , "Sharp-witted, intelligent" , "Smart, adroit" , "Smart or quick at learning" , "brilliant" .)