Chatterer's GP: one in West? (6)
I believe the answer is:
magpie
'chatterer's' is the definition.
(magpie can mean someone who chatters)
'gp one in west?' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'west?' becomes 'Mae' (actress Mae West).
'gp'+'i'='gpi'
'gpi' inserted into 'mae' is 'MAGPIE'.
(Other definitions for magpie that I've seen before include "Chatterbox" , "chatterer" , "Black and white bird, may be thieving" , "chatty bird" , "Bird - obsessive collector" .)