Ruthless Conservative line taken without regret (5)
I believe the answer is:
cruel
'ruthless' is the definition.
(thesaurus)
'taken without regret' is the wordplay.
'taken' becomes 'cl' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'regret' becomes 'rue' ('rue' can be a synonym of 'regret').
'cl' going around 'rue' is 'CRUEL'.
'conservative line' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for cruel that I've seen before include "Savage; harsh" , "Heartless" , "Vicious" , "Inflicting pain and feeling no concern" , "Sadistic, causing suffering" .)