Proper English throne overturned from long ago (8)
I believe the answer is:
primeval
'from long ago' is the definition.
(from the dawn of time)
'proper english throne overturned' is the wordplay.
'proper' becomes 'prim' (similar in meaning).
'english' becomes 'E' (abbreviation).
'throne' becomes 'lav' (both can informally mean toilet).
'overturned' says the letters should be written in reverse.
'lav' back-to-front is 'val'.
'prim'+'e'+'val'='PRIMEVAL'
(Other definitions for primeval that I've seen before include "Instinctive" , "Ancient" , "Very old" , "Prehistoric" , "From the earliest times" .)