Purge lists to block extremists on committee (7)
I believe the answer is:
cleanse
'purge' is the definition.
(thesaurus)
'lists to block extremists on committee' is the wordplay.
'lists' becomes 'leans' (I've seen this in other clues).
'to block' means one lot of letters goes inside another (block can mean to fill a hole in something).
'extremists on committee' becomes 'ce' (I can't justify this - if you can you should give a lot more credence to this answer).
'leans' going into 'ce' is 'CLEANSE'.
Can you help me to learn more?
(Other definitions for cleanse that I've seen before include "give absolution" , "Free of sin" , "Bathe" , "subject to purification" , "Disinfect" .)