Delegate's record in service (6)
I believe the answer is:
deputy
'delegate's' is the definition.
(I've seen this before)
'record in service' is the wordplay.
'record' becomes 'ep'.
'in' means one lot of letters goes inside another.
'service' becomes 'duty' (I've seen this before).
'ep' placed within 'duty' is 'DEPUTY'.
(Other definitions for deputy that I've seen before include "The next in command, replaces boss when necessary" , "Subordinate" , "One given the power to act for another" , "Assistant with power to act when alone" , "Assistant with power to act in the absence of superior" .)