Soldier authorised to raise gun offers top covering fire (11)
I believe the answer is:
mantelpiece
'top covering fire' is the definition.
'soldier authorised to raise gun offers' is the wordplay.
'soldier' becomes 'man' (I've seen this before).
'authorised' becomes 'let'.
'to raise' shows that the letters should be reversed in order.
'gun offers' becomes 'piece' (I can't justify this - if you can you should believe this answer much more).
'let' backwards is 'tel'.
'man'+'tel'+'piece'='MANTELPIECE'
Can you help me to learn more?
(Other definitions for mantelpiece that I've seen before include "Shelf over fireplace" , "Structure around a fireplace" , "Fireplace surround" , "place by fire?" .)