The contents of a well-used but badly flushed lavatory, the
bangers (sausages) being the turds and the
mash (mashed potato) being the bog
roll.
"Cinders and ashes, Thomas, your coaches are a disgrace", cried the Fat Controller. "There's soot all over the
windows, used tickets all over the
floor and Clarabel's khazi is full of
bangers and mash!"