Tough youth seen behind a conservative faked it (5)
I believe the answer is:
acted
'faked it' is the definition.
(act can mean to fake or pretend)
'tough youth seen behind a conservative' is the wordplay.
'tough youth' becomes 'Ted' (as in the Teddy Boy subculture).
'seen behind' means one lot of letters go next to another (some letters go behind others).
'conservative' becomes 'C' (UK political abbreviation).
'a'+'c'='ac'
'ted' put after 'ac' is 'ACTED'.
(Other definitions for acted that I've seen before include "Feigned" , "Appeared in play" , "Posed as" , "produced an effect" , "did something!" .)