Green’s Dictionary of Slang

impoverished.

1993		I. Welsh Trainspotting 227: The woman across the landing, a mumpy hoor as ah remember, opens her door.
2001		I. Welsh Glue 90: We head out n wir walkin wi a load ay mumpy Huns up tae the station.
2012		(con. 1980s) I. Welsh Skagboys 74: A bit ay a mumpy-faced auld cunt.