Scallywag upholding British accent (6)
I believe the answer is:
brogue
'accent' is the definition.
(brogue can mean a Scottish or Irish accent)
'scallywag upholding british' is the wordplay.
'scallywag' becomes 'rogue' (synonyms).
'upholding' is a charade indicator (letters next to each other) (holding on top - in a down clue).
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'rogue' after 'b' is 'BROGUE'.
(Other definitions for brogue that I've seen before include "Stout leather shoe" , "last work?" , "Decorated shoe; accent" , "Oxford" , "Outdoor shoe; accent" .)