Quite possibly, papers are on express (1,4,3)
I believe the answer is:
i dare say
'quite possibly' is the definition.
(I've seen this before)
'papers are on express' is the wordplay.
'papers' becomes 'ID' (identification papers).
'on' means one lot of letters go next to another.
'express' becomes 'say' (saying is a kind of expressing).
'id'+'are'+'say'='I DARE SAY'
(Other definitions for i dare say that I've seen before include "One assumes" , "It wouldn't surprise me" , "one might suppose" , "It's possible" , "Maybe" .)