Small Swiss bank given BP's business finds hidden dirt (7)
I believe the answer is:
subsoil
'dirt' is the definition.
(I know that subsoil is a type of dirt)
'small swiss bank given' is the wordplay.
'small swiss' becomes 'sub' (I am not sure about this - if you are sure you should believe this answer much more).
'bank' becomes 'soil bank' (soil bank is a kind of bank).
'given' says to put letters next to each other.
'sub'+'soil'='SUBSOIL'
'bp's business finds hidden' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for subsoil that I've seen before include "found under the bed" , "that's just below the surface?" , "may be dug up down under" , "Earth lying just under the surface" , "It's used to cultivate" .)