Fraud will be prosecuted, did you say? (5)
I believe the answer is:
pseud
'fraud' is the definition.
(I know that fraud can be written as pseud)
'be prosecuted did you say?' is the wordplay.
'be prosecuted' becomes 'sued' (I've seen this in another clue).
'did you say?' indicates a 'sounds like' (homophone) clue.
'sued' sounds like 'PSEUD'.
'will' acts as a link.
(Other definitions for pseud that I've seen before include "Poseur (colloq.)" , "Pretentious type" , "Socially pretentious person" , "Pretentious fraud" , "Fake intellectual" .)