Agent certain to carry round gun after end of war (9)
I believe the answer is:
'agent' is the definition.
(I know that surrogate is a type of agent)
'to carry round gun after end of war' is the wordplay.
'to carry' means one lot of letters goes inside another.
'round' becomes 'o' (round can mean a round object).
'gun' becomes 'gat' (US informal term for a gun).
'after end of war' becomes 'surre' (I can't explain this - if you can you should give a lot more credence to this answer).
'ogat' inserted within 'surre' is 'SURROGATE'.
'certain' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for surrogate that I've seen before include "Argues about rot with substitute or deputy" , "Substitute fulfilling the role of another" , "(A) substitute in office" , "stand-in" , "One standing in" .)