Petty Tory leader's sacking (8)
I believe the answer is:
trifling
'petty' is the definition.
(thesaurus)
'tory leader's sacking' is the wordplay.
'tory leader' becomes 't' (I've seen this in other clues).
'sacking' becomes 'rifling'.
't'+'rifling'='TRIFLING'
(Other definitions for trifling that I've seen before include "Of little importance" , "insignificant" , "Minor" , "Dallying; petty" , "Unimportant, trivial" .)