It's difficult to top Christmas Tree with the pocket money that's available? (4,4)
I believe the answer is:
hard cash
'the pocket money that's available?' is the definition.
I can't judge whether this defines the answer.
'it's difficult to top christmas tree' is the wordplay.
'it's difficult' becomes 'hard' ('hard' can be a synonym of 'difficult').
'to top' suggests taking the first letters.
'tree' becomes 'ash' (ash tree is a kind of tree).
The first letter of 'christmas' is 'c'.
'hard'+'c'+'ash'='HARD CASH'
'with' is the link.
Can you help me to learn more?
(Other definitions for hard cash that I've seen before include "Ready money" , "Coins and banknotes - not a cheque" , "Coins and notes, not cheques or promises" , "Not plastic!" .)