Green’s Dictionary of Slang

biscuits and cheese n.

the knees.

1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
2001		M. Coles Bible in Cockney 67: There was this geezer who had leprosy (some dodgy skin disease), and he came to Jesus, fell on his biscuits and said, ‘If you want to, please make me clean’.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.