Green’s Dictionary of Slang

1. (UK WWI ) a flea [anti-German var. on Scotch greys under Scotch adj.].

1921

N&Q 12 Ser. IX 466: Prussian Guard. A flea.

2. a card, esp. a bingo card [rhy. sl.].

1937–84		Partridge DSUE.
1960		J. Franklyn Dict. Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1992		R. Puxley Cockney Rabbit.