Prisoner has left silver (3)
I believe the answer is:
lag
'prisoner' is the definition.
(slang term)
'left silver' is the wordplay.
'left' becomes 'l' (common abbreviation).
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'l'+'ag'='LAG'
'has' acts as a link.
(Other definitions for lag that I've seen before include "Dawdle" , "Drag one's feet" , "Cover pipes" , "Old convict - dally - insulate" , "Wrap to protect from frost" .)