Currency left after rest damaged in battering (5,8)
I believe the answer is:
pound sterling
'damaged in battering' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'currency left after rest' is the wordplay.
'currency' becomes 'pound' (I have seen 'Egyptian currency ' mean 'pound' so perhaps 'currency' could also mean 'pound').
'left after rest' becomes 'sterling' (I can't justify this - if you can you should give a lot more credence to this answer).
'pound'+'sterling'='POUND STERLING'
Can you help me to learn more?
(Other definitions for pound sterling that I've seen before include "Tender" , "UK currency" .)