Admit the French metal (3,2)
I believe the answer is:
let in
'admit' is the definition.
(I know that admit can be written as let in)
'the french metal' is the wordplay.
'the french' becomes 'le' ('the' in French).
'metal' becomes 'tin' (tin is a kind of metal).
'le'+'tin'='LET IN'
(Other definitions for let in that I've seen before include "Admit" , "swindle . . ." , "Allow to enter" , "Allowed to enter" , "Grant entry" .)