What the parliamentarians do when support is dead and gone (9)
I believe the answer is:
legislate
'what the parliamentarians do when support' is the definition.
The definition suggests a singular noun but the answer is not.
'is dead and gone' is the wordplay.
'dead' becomes 'late' (similar in meaning).
'and' is a charade indicator (letters next to each other).
'gone' becomes 'leg' (I can't explain this - if you can you should give a lot more credence to this answer).
'is'+'late'='islate'
'islate' after 'leg' is 'LEGISLATE'.
Can you help me to learn more?
(Other definitions for legislate that I've seen before include "Make provision" , "Pass laws" , "Pass through the house" , "Establish rules" , "put in force" .)