Writer and politician returned model on time (10)
I believe the answer is:
librettist
'writer' is the definition.
(I know that librettist is a type of writer)
'politician returned model on time' is the wordplay.
'politician' becomes 'lib'.
'returned' says the letters should be written backwards.
'model' becomes 'sitter' (I've seen this before).
'on time' becomes 't' (abbreviation. I am not sure about the 'on' bit.).
'sitter' backwards is 'rettis'.
'lib'+'rettis'+'t'='LIBRETTIST'
'and' is the link.
Can you help me to learn more?
(Other definitions for librettist that I've seen before include "Deviser of book" , "Provider of opera's words" .)