Revolutionary chamber left space in capital (10)
I believe the answer is:
metropolis
'capital' is the definition.
(I've seen this before)
'revolutionary chamber left space' is the wordplay.
'revolutionary' says the letters should be written in reverse.
'chamber' becomes 'silo' (chamber holding a missile).
'left' becomes 'port' (left side of a ship - opposite of starboard).
'space' becomes 'em' (in typography, a space as wide as a letter 'm').
'silo'+'port'+'em'='siloportem'
'siloportem' in reverse letter order is 'METROPOLIS'.
'in' acts as a link.
(Other definitions for metropolis that I've seen before include "chief centre" , "See" , "centre of activity" , "Urban centre" , "London, say" .)