Groom about to interrupt writer (5)
I believe the answer is:
preen
'groom' is the definition.
(a bird grooms itself by preening feathers)
'about to interrupt writer' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to interrupt' is an insertion indicator.
'writer' becomes 'pen' (something which writes).
're' placed inside 'pen' is 'PREEN'.
(Other definitions for preen that I've seen before include "Maintain" , "Groom elaborately" , "(Of a bird) tidy and clean feathers" , "Groom (oneself) with evident vanity" , "setdown straight?" .)