The poem Ella is reading to Tabitha in the film's opening scene is the classic "The Raven" by Edgar Allan Poe. The poem was originally published in January 1845.
André Morell played the title character in the 1958 TV series of Quatermass and the Pit (1958), and Barbara Shelley was one of the main characters in the 1967 film version, Uma Sepultura na Eternidade (1967) (aka Five Million Years to Earth).
Although this was made by Hammer Films, the name "Hammer" appears nowhere in the credits.
William Lucas co-starred in another Hammer film, X THE UNKNOWN.