Derek briefly in charge at German city food shop (12)
I believe the answer is:
delicatessen
'food shop' is the definition.
('delicatessen' can be a synonym of 'food shop')
'derek briefly in charge at german city' is the wordplay.
'derek briefly' becomes 'del'.
'in charge' becomes 'ic'.
'german city' becomes 'essen' (I've seen this before).
'del'+'ic'+'at'+'essen'='DELICATESSEN'
(Other definitions for delicatessen that I've seen before include "Shop selling unusual or foreign prepared food" , "Shop selling specialist foods" , "Unusual foods here" , "Specialised food shop" , "Here one gets exotic foods" .)