The poster quote "People of Earth. Your planet is about to be destroyed... We're terribly sorry for the inconvenience" is a reference to the Vogon Destructor Fleet from Douglas Adams' The Hitchhiker's Guide to the Galaxy, who broadcast "People of Earth, your attention, please. [...] regrettably, your planet is one of those scheduled for demolition. The process will take slightly less than two of your Earth minutes. Thank you. ... ", before destroying the Earth.
The Doctor's line, "Who was it said; 'Earthmen never invite their ancestors round to dinner?'" is a reference to the Hitchhiker's Guide to the Galaxy line, "Earthmen are not proud of their ancestors and never invite them 'round to dinner."