Enterprise shown by Labour leader? Nonsense! (6)
I believe the answer is:
drivel
'nonsense' is the definition.
(drivel can mean nonsensical speech or writing)
'enterprise shown by labour leader?' is the wordplay.
'enterprise' becomes 'drive' (I can't justify this - if you can you should give a lot more credence to this answer).
'shown by' means one lot of letters go next to another.
'labour leader?' becomes 'l' (the leading letter of 'labour').
'drive'+'l'='DRIVEL'
Can you help me to learn more?
(Other definitions for drivel that I've seen before include "Foolishness" , "Stupid talk" , "Slaver" , "Worthless, foolish nonsense" , "Nonsense, garbage" .)