Time a backbencher, say, gets involved in study about taxation (5,4)
I believe the answer is:
stamp duty
'taxation' is the definition.
(stamp duty is a kind of taxation)
'time a backbencher say gets involved in study' is the wordplay.
'time' becomes 't' (abbreviation).
'a backbencher say' becomes 'amp' (I can't explain this - if you can you should believe this answer much more).
'gets' is an insertion indicator.
'involved in' is an anagram indicator (involved can mean complex or confusing).
't'+'amp'='tamp'
'study' is an anagram of 'sduty'.
'tamp' put within 'sduty' is 'STAMP-DUTY'.
'about' is the link.
Can you help me to learn more?
(Other definitions for stamp duty that I've seen before include "Tax paid on legal documents" , "House purchase levy" , "Tax receipted by affixing paper seal to deed" , "Tax collected on legal documents" , "House-buying tax" .)