Doctor Who/Recap/S27/E05 World War Three

I think you'll find the Prime Minister is an alien in disguise, and... That’s never gonna work, is it?

—The Doctor

When we left the Doctor and Rose, they were in 10 Downing Street in the company of a passel of aliens and Harriet Jones (MP, Flydale North).

Rose and Harriet play a bit of hide and seek with two of the Slitheen, but are saved when the Doctor enters with a fire extinguisher and sprays the aliens into submission. The three allies run for the conference room, updating each other on the sitch en route; once they've made it to the conference room, the Doctor activates a switch that seals them in, cosily, behind three inches of steel armor.

Mickey calls Rose's superphone and brings her up to speed: the acting Prime Minister, whom they know to be a disguised Slitheen, has asked the UN to give him the nuclear launch codes. He claims that it's to shoot at the aliens, but the Doctor is not fooled and deduces its true purpose: the Slitheen will divert the nukes and wreak radioactive havoc on Earth. Once the planet's been reduced to inhospitable slag, they'll sell what remains as fuel—there's a recession out there, and people are buying cheap. Jackie, in the background, is wailing about her daughter's safety.

Rose tells her mum to knock off the Mama Bear business, and the Doctor walks Mickey through the process of hacking into UNIT, hijacking a submarine and firing a missile at 10 Downing Street. It gets pounded into rubble; the Doctor, Rose, and Harriet are saved by the steel-plated conference room and Harriet Jones (MP, Flydale North) takes charge of the situation and calls off the nukes. The Doctor recognizes her now: she'll soon be Harriet Jones (Prime Minister), elected for three consecutive terms and the champion of the Golden Age of Britain.

Although Britain's safe for now, this is far from the last we'll see of the Slitheen and of Harriet Jones (Prime Minister).

Tropes

Agent Scully: The human race turns out to be this at the end of the episode—despite incontrovertible proof of alien life, the media quickly dismisses the whole incident as a hoax.
Call Back: The "He's got a northern accent!"/"Lots of planets have a north..." exchange from the season premiere is replicated between Harriet and Rose.
Curse Cut Short: "Oh, bol-"
Does This Remind You of Anything?: The rather blatant references to the Iraq war (massive weapons of destruction).
- The Slitheen plan also bears some similarities to conspiracy theories surrounding 9/11 claiming that elements within the government engineered a plane crash into a major national monument for nefarious, power-grabbing ends.
Early Installment Weirdness: The first appearance of the Slitheen is very different from later versions, most notably how they blow up. In later explosions, it looks like actual slime, whereas this time, it had a texture more like overcooked spaghetti in lime gelatin.
Fire-Forged Friends: Mickey and Jackie
"Friend or Idol?" Decision: "I could save the world but lose you!"
Gasshole: The Slitheen. All of them.
Hollywood Hacking: Mickey launching the missile into Downing Street.
- He does need an actual password provided by the Doctor. However, no way a military organization would use a single common word as the one thing stopping civilians from launching missiles.
  - However he is using a 'Back-Door' that almost nobody else knows about.
Lampshade Hanging: The Slitheen are delighted to see that "The telephone is actually red!"
Mama Bear: Jackie
The Password Is Always Swordfish: an especially Egregious case, as the password to every non-nuclear UN-controlled missile launch platform turns out to be "buffalo", a few times over.
- The suggestion seemed to be that "buffalo" was a special password for UNIT types to bypass security.
  - And that The Doctor, having worked for UNIT around the time that the whole world decided this computer thing was really going to take off may have built in the back-door himself.
Shown Their Work: Not only did they have the proper prefix for a submarine-launched Harpoon missile, they CGed a very good replica of a Harpoon.
- However, Harpoons are anti-ship missiles, not land attack.
The Siege: The Doctor, Rose and Harriet barricade inside an office with steel-reinforced walls.
Toilet Humour: The Slitheen. Again.
Weaksauce Weakness: The Slitheen explode on contact with a mixture of concentrated vinegar and pickled onions. Granted, the Doctor implies that this only works with Slitheen that have recently been using a body-compression disguise, but it does seem a bit silly that such a Slitheen could die by falling into a bowl of salad.
- In a later episode, "Boom Town", it is mentioned that the Raxicoricofallapatorian death penalty involves being lowered into a vat of acetic acid, so the weakness probably applies to all of them at any time (granted, in a larger quantity).
Whitehall: 10 Downing Street.