Handle at last on copper pot with this (3)
I believe the answer is:
cue
'pot with this' is the definition.
(used to pot balls in snooker, pool etc)
'handle at last on copper' is the wordplay.
'at last' indicates one should take the final letters.
'on' is a charade indicator (letters next to each other).
'copper' becomes 'cu' (chemical symbol).
The final letter of 'handle' is 'e'.
'e' after 'cu' is 'CUE'.
(Other definitions for cue that I've seen before include "Used in snooker and on stage" , "Hint on stage" , "Billiards stick" , "Signal (to actor)" , "Signal for action" .)