Like the novel, the meaning of the title is two-fold, and a play on words. First, the plot centres around Scottish Detective Sergeant Bruce Robertson. It should be noted that 'filth' is a slang term for the police in the UK, used mainly as a pejorative and often in the criminal underworld. The name also directly refers to the depraved and frankly disgusting behaviour of the protagonist.
Indeed, the contents of the novel, and undoubtedly the upcoming film adapation, is akin to filth.