Comprehensive teacher knocked back by somebody without guts in assembly (7,5)
I believe the answer is:
general synod
'assembly' is the definition.
(assembly of members of the Church of England)
'comprehensive teacher knocked back by somebody without guts' is the wordplay.
'comprehensive' becomes 'general' (general can mean comprehensive or universal).
'teacher' becomes 'don' (don is a kind of teacher).
'knocked back' shows that the letters should be reversed in order.
'by' is a charade indicator (letters next to each other).
'without guts' suggests removing the centre (the guts of the word are removed).
'somebody' with its centre taken out is 'sy'.
'don' backwards is 'nod'.
'nod' put after 'sy' is 'synod'.
'general'+'synod'='GENERAL SYNOD'
'in' acts as a link.
(Another definition for general synod that I've seen is " Angels yonder (anag) -- governing body of the Church of England".)