Left in charge of old colonnade (7)
I believe the answer is:
portico
'colonnade' is the definition.
(I've seen this before)
'left in charge of old' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'in charge of' becomes 'ic'.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'port'+'ic'+'o'='PORTICO'
(Other definitions for portico that I've seen before include "gallery, perhaps" , "Arcade" , "Classical porch" , "Covered entrance with columns" , "building construction" .)