Dog I would put in the Foreign Office (4)
I believe the answer is:
fido
'dog' is the definition.
(I know that Fido is a fictional dog)
'i would put in the foreign office' is the wordplay.
'i would' becomes 'I'd'.
'put in' indicates putting letters inside.
'the foreign office' becomes 'FO' (abbreviation).
'id' placed inside 'fo' is 'FIDO'.
(Other definitions for fido that I've seen before include "it would disperse fog" , "Dog perhaps" , "Fog disperser" , "Typical dog's name" .)