Green’s Dictionary of Slang

foaming adj.

an intensifier; a euph. for fucking adj.

Bystander (London) 17 Dec. 3/1: ‘No, I ain’t got no (foaming) use fer new-fangled notions’.
[UK]D. Abse In the Cage (1967) 124: Hey, ey. Nark it. Manners. Where’s your foaming manners.