Green’s Dictionary of Slang

1. (UK Und.) a banknote, usu. of £5 and up.

1950

P. Tempest Lag’s Lex. 53: crackle. Bank-notes. Five pounds and upwards.

2. empty, foolish chattering.

1978

S. Longstreet Straw Boss (1979) 272: ‘Cut the crackle,’ said Mike.