Expose Sunak suspiciously hiding millions (6)
I believe the answer is:
unmask
'expose' is the definition.
(I know that expose is a is a kind of of unmask)
'sunak suspiciously hiding millions' is the wordplay.
'suspiciously' indicates an anagram (I've seen this in other clues).
'hiding' indicates putting letters inside.
'millions' becomes 'm' (abbreviation).
'sunak' anagrammed gives 'unask'.
'unask' enclosing 'm' is 'UNMASK'.
(Other definitions for unmask that I've seen before include "show his face" , "establish identity" , "Reveal true identity of" , "Expose, strip away concealment" , "Discover the identity of" .)