Liberal showing no mercy (9)
I believe the answer is:
unsparing
This clue is a double definition.
'liberal' is the first definition.
(e.g. when adding something to something)
'showing no mercy' is the second definition.
(Other definitions for unsparing that I've seen before include "Profuse - ruthless" , "Wanting mercy" , "Merciless, severe" , "harsh" , "generous" .)