Penny replaced one percent RRP nominal fee (10,4)
I believe the answer is:
peppercorn rent
'nominal fee' is the definition.
The definition suggests a singular noun which matches the answer.
'penny replaced one percent rrp' is the wordplay.
'penny' becomes 'p' (short for pence).
'replaced' is an anagram indicator.
'one'+'percent'+'rrp'='onepercentrrp'
'onepercentrrp' with letters rearranged gives 'eppercornrent'.
'p'+'eppercornrent'='PEPPERCORN RENT'
Can you help me to learn more?
(Other definitions for peppercorn rent that I've seen before include "nominal charge" , "cost of cheap accommodation" .)