Particularly when it’s over a couple of pounds (5,3)
I believe the answer is:
above all
'particularly' is the definition.
(thesaurus)
'it's over a couple of pounds' is the wordplay.
'it's over' becomes 'above' (I've seen this before).
'couple of' shows that letters should be duplicated.
'pounds' becomes 'L' (abbreviation e.g. Lsd - pounds, shillings, pence).
'l' duplicated is 'll'.
'above'+'a'+'ll'='ABOVE ALL'
'when' is the link.
(Other definitions for above all that I've seen before include "Hamlet : 'This . . . . . . . ., to thine own self be true'" , "Notably" , "at the end of the day?" , "First and foremost" , "Like the managing director" .)