A conservative in post gets rise (6)
I believe the answer is:
ascend
'rise' is the definition.
(synonyms)
'a conservative in post' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'in' indicates putting letters inside.
'post' becomes 'send' (synonyms).
'c' placed into 'send' is 'scend'.
'a'+'scend'='ASCEND'
'gets' acts as a link.
(Other definitions for ascend that I've seen before include "Move upwards" , "Travel upwards" , "Get higher" , "Come up" , "Climb, go up (6)" .)