The Nightmare Man

If you know your telefantasy, you'll instantly spot the clues which signify this as a masterpiece: directed by Douglas Camfield, scripted by Robert Holmes, and featuring a top-rank cast that includes Celia Imrie, James Warwick, Maurice Roëves and Jonathan Newth. A slavering, monstrous creature runs loose on a remote Scottish island, killing the residents and emitting a dangerous radiation. Could the Child of Vodyanoi really be an extra-terrestrial? Or is the monster a poorly-kept military secret?