Redesigned flat incorporates universal defect (5)
I believe the answer is:
fault
'defect' is the definition.
(I know that defect can be written as fault)
'redesigned flat incorporates universal' is the wordplay.
'redesigned' is an anagram indicator.
'incorporates' means one lot of letters goes inside another.
'universal' becomes 'U' (film certificate).
'flat' anagrammed gives 'falt'.
'falt' enclosing 'u' is 'FAULT'.
(Other definitions for fault that I've seen before include "Censure" , "Defect, mistake" , "Blame" , "Flaw - defect" , "Defect or offence" .)