Rising cheers surrounding Conservative legislation (3)
I believe the answer is:
act
'legislation' is the definition.
(I've seen this in another clue)
'rising cheers surrounding conservative' is the wordplay.
'rising' is a reversal indicator (letters written upwards in a down clue).
'cheers' becomes 'ta' (both can mean thank you).
'surrounding' is an insertion indicator.
'conservative' becomes 'C' (UK political abbreviation).
'ta' going around 'c' is 'tca'.
'tca' in reverse letter order is 'ACT'.
(Other definitions for act that I've seen before include "Take part in a play" , "Thing done" , "Perform - part of a play" , "Do something, in a play?" , "Major division of play" .)