Green’s Dictionary of Slang

(Irish) respectable; esp. in phr. the parliamentary side of one’s arse.

1920		in R. Ellman Joyce (1983) 474: Lent the chapter to one or two people but they know as much about it as the parliamentary side of my arse.
1922		Joyce Ulysses 327: Arrah, sit down on the parliamentary side of your arse for Christ’ sake and don’t be making a public exhibition of yourself.