Oranges and Lemons

"" was a rhyme that Joe Buchanan once recited in part, saying, "Here comes a candle to light you to bed, here comes a chopper to chop off your head". (TV: The God Complex)

Behind the scenes
It is also obliquely referenced by the episode title The Bells of Saint John, as one of the rhyming couplets from the original nursery rhyme goes "Pokers and tongs / say the bells of Saint John's".