Secret agent drinking cold liquor and strong cider (7)
I believe the answer is:
scrumpy
'strong cider' is the definition.
(I've seen this before)
'secret agent drinking cold liquor' is the wordplay.
'secret agent' becomes 'spy' (spy is a kind of secret agent).
'drinking' is an insertion indicator.
'cold' becomes 'c' (eg on taps).
'liquor' becomes 'rum' (rum is a kind of liquor).
'c'+'rum'='crum'
'spy' enclosing 'crum' is 'SCRUMPY'.
'and' is the link.
(Other definitions for scrumpy that I've seen before include "rough drink" , "Strong or dry cider" , "Strong English cider" , "Rough strong cider" , "Strong drink" .)