Green’s Dictionary of Slang

(UK und.) a £5 note.

[1894		N. Dakota Jrnl 25 May n.p.: Erik Ramstead left for a six weeks visit [...] His objective point is Tennessee — where he expects to invest some good hard ‘panga’].
1936		J. Curtis Gilt Kid n.p.: ‘A fiver. Five pounds, five nicker, five quid, five oncers, pangy bar.
1950		P. Hoskins No Hiding Place! 191/2: Pangy bar. £5.