Flesh and Stone
Regarding an unanswered question (from a child) of why a gigantic robot in London 1851 "isn't in the history books", Davies and Gardner jokingly offer several possibilities ranging from there being alternate history of "Doctor Who" England, pointing out "a spaceship didn't fly into the Big Ben in 2006 either" (in the episode "Aliens of London") or that perhaps "maybe everyone was retconned by the soon-to-be-born Torchwood, or something." A line in Steven Moffat's series 5 episode "Flesh and Stone" has the Doctor recall the Cyberking's rampage, attributing history's failure to record it to the cracks in time and space that are causing time to be unwritten.