Cunning and very posh, the French will conceal banking info (7)
I believe the answer is:
vulpine
'cunning' is the definition.
(I've seen this before)
'very posh the french will conceal banking info' is the wordplay.
'very' becomes 'v' (abbreviation).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'the french' becomes 'le' ('the' in French).
'will conceal' means one lot of letters goes inside another.
'banking info' becomes 'PIN'.
'le' enclosing 'pin' is 'lpine'.
'v'+'u'+'lpine'='VULPINE'
'and' is the link.
(Other definitions for vulpine that I've seen before include "like Basil Brush?" , "Relating to foxes" , "Liven up in fox-like way" , "Like a fox -- liven up (anag)" , "Resembling a fox" .)