Doctor Who Series 10: 12 Easter Eggs & References You Might've Missed In "Knock Knock'

Due to the Landlord's strange behaviour, the Doctor checks his mental faculties by asking him who the Prime Minister is. "Margaret Thatcher? Harriet Jones?" he lists. "Wilson? Eden?"

The name that will pop out of those to Doctor Who fans is, of course, Harriet Jones. As played by Penelope Wilton, Harriet Jones (you know who she is) rose to power after helping the Ninth Doctor and Rose stop the Slitheen in 2005's Aliens of London. Unfortunately for her, her fire-first attitude to the Sycorax in the same year's The Christmas Invasion meant that the Doctor himself brought her administration to a premature end with just six words: "Don't you think she looks tired?"

It's odd that the Doctor doesn't mention another former Prime Minister here - namely, Harold Saxon, the alias the Master used when he stepped into Downing Street in 2007's The Sound of Drums. It would have been a good way to remind audiences of John Simm's Master before he returns later this season.