FILTH, in his heyday, was an international lawyer with a practice in the Far East. Now, only the oldest QCs and Silks can remember that his nickname stood for Failed In London Try Hong Kong. Long ago, Old Filth was a Raj orphan - one of the many young children sent 'Home' from the East to be fostered and educated in England. Jane Gardam's new novel tells his story, from his birth in what was then Malaya to the extremities of his old age.