1 No Place Like Home
When the copper Slitheen visits Mickey's flat in "World War III", the word "Salford" is graffitied on the wall near the elevator. Christopher Eccleston was born in Salford.
2 Pub Quiz
In "Father s Day” Suzie complains that, “There's no one from the Lamb and Flag!” The Lamb and Flag was a pub in “Bottom” the sitcom starring and written by Rik Mayall and Adrian Edmondson.
3 Venomous Remark
In "Boom Town" Margaret Blaine comments that, “If I’d refused, my father would have fed me to the venom grubs.
Venom Grubs were previously seen way back in the 1965 story “The Web Planet".
in "Boom Town" Rose mentions to Mickey that she and the Doctor have visited Justica. Justica was also the name of a prison planet in the original Doctor Who novel Monsters Inside by Stephen Cole.
5 I Swear I’ve Heard That Before
In "Bad Wolf" one of the Weakest Link questions contains the phrase "Who went out with the "Grexnix" in the holo-drama...?" Grexnix was a swear word used by the Mighty Tharg in 2000AD. The word "ghafflebette" is used in another questions; this is also from 2000ad but means something along the lines of awesome.
"Ahh, not bad for a man in his Jim-Jams. Very Arthur Dent, now there was a nice man,” says the Doctor in "The Christmas Invasion, which is more of an in-joke than it might first appear. Dent was, of course, the everyman character in The Hitchhiker’s Guide To The Galaxy, but that book was also written by a former Doctor Who script editor, Douglas Adams. Don’t go thinking about how that blurs the line between reality and fiction, you might just vanish in a puff of illogic…
In "New Earth" the Duke of Manhattan is dying from Petrifold Regression — a disease that turns its victims to stone — which is also mentioned in the Tenth Doctor Adventures novel The Stone Rose by Jacqueline Rayner.
8 Dr Jamie
The Doctor introduces himself as Dr James McCrimmon in "Tooth and Claw" eschewing his usual nom de plume of John Smith for the name of one of his former companion (from the Troughton era).
9 By Zeus
In "the Girl In The Fireplace" The Doctor wonders, "Zeus plugs. Where are my Zeus plugs? I had them a minute ago, I was using them as castanets." He was last seen using Zeus plugs to repair the TARDIS just before he said goodbye to Sarah Jane Smith at the end of the fourth Doctor story "The Hand of Fear".
10 Electric Dreams
A lorry in "The Rise Of The Cybermen" is emblazoned with the logo for International Electromatic. This company originally featured in the second Doctor Who Cyberman story "The Invasion".
11 The In-Joke In The High Castle
In "The Impossible Planet" Scootie is given the designation "PKD". These are the initials of infamous SF writer Philip K Dick (author of Do Androids Dream Of Electric Sheep? And The Man In The High Castle.
12 Ice Ice Baby
Is this an in-joke or just a coincidence? In "The Impossible Planet" – a story rife with 666 allusions – the song "Bolero" is being pumped through the space station at one point. "Bolero" was the music that Torville and Dean skated to when they received across the board record marks of 6 from every judge at the 1984 Winter Olympics.
13 Why Don’t You
Long before revamping Doctor Who, Russell T Davies was once a producer on the children’s magazine show Why Don’t You (Just Switch Off You Television Set And Go And Do Something Less Boring Instead – something which he clearly hopes you won’t do these days). For that show he created the "Liverpool Investigation 'n' Detective Agency". This had transmuted into the "London Investigation 'n' Detective Agency" (LINDA) by the time of "Love & Monsters".
14 Fake That
An in-joke you wouldn’t have seen on screen during the episode, but which was one of the most elaborate the production team ever produced nonetheless. Because for legal reasons real notes could not be used in the cash point sequence in "The Runaway Bride" the production team made fake banknotes for the scene. The £10 notes featured The Doctor's face and the phrases “I promise to pay the bearer on demand the sum of ten satsumas" and "No second chances — I'm that sort of a man". The £20 notes featured producer Phil Collinson and the phrase "There's no point being grown up if you can't be a little childish sometimes" paraphrasing the Fourth Doctor in "Robot".
15 Next Week Gag
In the trailer for "The Shakespeare Code" that came at the end of "Smith And Jones" there’s a brilliantly witty piece of editing. A clip of Shakespeare saying, "Hey nonny, nonny!" cuts straight to a clip of another character crying, "Nooooooooo!"
In "Gridlock" traffic reporter Sally Calypso is a deliberate homage to Swifty Frisko the automated newsreader in the 2000AD comic story The Ballad of Halo Jones.
17 Home Sweet Home
Wester Drumlins, the name of the dilapidated house in "Blink", was the name of a house in which the story’s writer Steven Moffat once lived.
18 Little Reference
In "The Sound Of Drums" the Master mutter, “Britain, Britain, Britain...” mirroring Tom Baker’s narrations from Little Britain.
19 Speaka Da Lingo
In "The Unicorn And The Wasp" Donna puts on a posh accent: "Good afternoon, my Lady. Topping day, what? Spiffing. Top ho!" To which the Doctor responds, “No, no, no, no, no, no, no, no. Don't do that. Don't." He had to similarly convince Rose not to attempt a Scottish accent in "Tooth And Claw" and Martha not to speak Shakespearean in "The Shakespeare Code".
20 Creative Accounting
By some systems of counting "Planet Of The Dead" could be considered Doctor Who’s 200th story (if you count Shada, for example, and "The Trial Of A Time Lord" as four separate stories). That’s why the bus in "Planet Of The Dead" is the 200.
21 Life On Mars
The Bowie Base in "The Waters Of Mars" is, of course, named after David Bowie, singer of "Life On Mars".