Daft as a brush
This rather quaint British expression describing someone as mad or silly has a gentle, almost affectionate connotation. Its origin is obscure. Brewer’s Dictionary of Phrase and Fable attributes it to a catchphrase coined by comedian Ken Platt who adapted it from the North of England expression soft as a brush. Ken Platt attested to this in a radio interview in 1979 when he said he used the expression in shows during the 1940s and people would correct him by saying it should be soft as a brush. Eric Partridge on the other hand maintains that it is an abbreviation of daft as a brush without bristles, which was in use during the 1920s. One thing is for sure; it has nothing to do with Victorian child chimney sweeps. This spurious etymology maintains that child chimney sweeps were plunged head first down chimneys and so became daft as their own brushes.