Struggle to accept Labour's leader is perfect (8)
I believe the answer is:
complete
'is perfect' is the definition.
(similar in meaning)
'struggle to accept labour's leader' is the wordplay.
'struggle' becomes 'compete' (I've seen this before).
'to accept' means one lot of letters goes inside another.
'leader' suggests taking the first letters.
The first letter of 'labours' is 'l'.
'compete' enclosing 'l' is 'COMPLETE'.
(Other definitions for complete that I've seen before include "Bring to a satisfactory end" , "Bring to a finish" , "Whole, nothing missing" , "Finished - whole" , "whole,entire,uncut" .)