Crikey, I'm not sure British Standard is applied to credit (6)
I believe the answer is:
crumbs
'crikey' is the definition.
(both are expressions of shock)
'i'm not sure british standard is applied to credit' is the wordplay.
'i'm not sure' becomes 'um' (expression of hesitation).
'british standard' becomes 'BS' (legal abbreviation).
'is applied to' says to put letters next to each other.
'credit' becomes 'cr' (abbreviation).
'um'+'bs'='umbs'
'umbs' after 'cr' is 'CRUMBS'.
(Other definitions for crumbs that I've seen before include "not much of a bloomer!" , "Exclamation of surprise" , "Crikey, cripes" , "Tiny bits of bread - golly!" , "Blimey!" .)