Able to pay up five pound in notes, perhaps (7)
I believe the answer is:
solvent
'able to pay' is the definition.
(thesaurus)
'up five pound in notes perhaps' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'five' becomes 'v' (roman numeral).
'pound' becomes 'l'.
'in' is an insertion indicator.
'perhaps' indicates an anagram.
'v'+'l'='vl'
'vl' backwards is 'lv'.
'notes' is an anagram of 'soent'.
'lv' placed into 'soent' is 'SOLVENT'.
(Other definitions for solvent that I've seen before include "ether?" , "liquid chemical" , "Glue" , "not on the rocks" , "In the black - liquefier" .)