 She did stage work and appeared on TV in episodes of "Agatha Christie's Poirot" and "Casualty" (1993) before landing the role of Penhaligon in "Cracker", which she held from the show's inception in 1993 until its demise in 1995 and became one of the most memorable characters of the series.Somerville played Lady Stockbridge in Julian Fellowes's "Gosford Park" and Harry Potter's mother Lily in all the "Potter" movies.In May 2007, she played author Daphne du Maurier in the BBC TV drama "Daphne".