Expert on the fiddle in business, one banking on a couple of pounds (7)
I believe the answer is:
corelli
'expert on the fiddle' is the definition.
The definition suggests a singular noun which matches the answer.
'business one banking on a couple of pounds' is the wordplay.
'business' becomes 'co' (short for company).
'one banking' becomes 'rei' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'on' indicates putting letters inside (as in clothing 'on' a person).
'a couple of' shows that letters should be duplicated.
'pounds' becomes 'l' (abbreviation e.g. Lsd - pounds, shillings, pence).
'l' duplicated is 'll'.
'rei' placed around 'll' is 'relli'.
'co'+'relli'='CORELLI'
'in' is the link.
Can you help me to learn more?
(Other definitions for corelli that I've seen before include "Arcangelo, seventeenth to eighteenth century Italian composer, violinist" , "A mandolin-playing Captain" , "Arcangelo --, Italian baroque composer" , "Captain -'s Mandolin (de Bernires)" , "Marie - - , romantic 17" .)