In the Foreign Office, short measure of sherry (4)
I believe the answer is:
fino
'sherry' is the definition.
(I've seen this before)
'in the foreign office short measure' is the wordplay.
'in the' means one lot of letters goes inside another.
'foreign office short' becomes 'FO' (abbreviation; 'short' asks for a short form).
'measure' becomes 'in' (in is a kind of measure).
'fo' placed around 'in' is 'FINO'.
'of' acts as a link.
(Other definitions for fino that I've seen before include "Bone dry sherry, served chilled" , "Light-coloured sherry" , "Driest of the sherries" , "Light dry sherry" , "Type of sherry" .)