Pretend the pound note is coming back (3,2)
I believe the answer is:
let on
'pretend' is the definition.
(I've seen this before)
'pound note is coming back' is the wordplay.
'pound' becomes 'L' (the pound sign is based on an L).
'is coming back' says the letters should be written in reverse.
'note' reversed gives 'eton'.
'l'+'eton'='LET ON'
'the' is the link.
(Other definitions for let on that I've seen before include "Reveal, divulge" , "Allow to board, or pretend" , "Tell me" , "Pretend informally or permit to board" , "Divulge info; pretend" .)