Left with additional bit of silver in reserve capital (4,7)

I believe the answer is:

port moresby

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'capital' is the definition.
(capital of Papua New Guinea)

'left with additional bit of silver in reserve' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'with additional bit of silver' becomes 'mores' (I can't explain this - if you can you should believe this answer much more).
'in reserve' becomes 'by' (synonyms).
'port'+'mores'+'by'='PORT MORESBY'

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