Hand over vessel with metal coating (4,2)
I believe the answer is:
turn in
'hand over' is the definition.
(both can mean to surrender or give up something)
'vessel with metal coating' is the wordplay.
'vessel' becomes 'tin' (I've seen this in other clues).
'with' means one lot of letters goes inside another.
'metal coating' becomes 'urn' (I am not sure about this - if you are sure you should believe this answer much more).
'tin' enclosing 'urn' is 'TURN-IN'.
(Other definitions for turn in that I've seen before include "rat on" , "Hand over - retire" , "Informally, go to bed or hand over" , "Prepare for sleep" , "Surrender" .)