World Enough and Time

I think maybe four percent of the population even knows what curling is

Not a heavy Scottish population, then?

UNIT is a huge paramilitary organization in the Doctor Who universe, dating back to classic days when the Doctor (I've no idea which one or which ones) had a friend who was in charge of it, named the Brigadier. UNIT has turned up in both Torchwood and series 4 Doctor Who now. It always reminds me of S.H.I.E.L.D., and they have (or had) a huge flying battleship called the Valiant that looks remarkably like the SHIELD Helicarrier.

Anyway, UNIT is the Unified Taskforce (I think) and Martha Jones now works for them. The UNIT soldiers wear red caps, and their mandate is to fight enemy aliens.

So when Martha Jones comes to Torchwood there's a conversation that goes like this:

JACK: Dr Jones is from UNIT.
GWEN: Oh, I'm sorry, sorry, I get a bit confused. Which one's UNIT?
JACK: Intelligence, military, cute red caps. The acceptable face of intelligence gathering on aliens. We're more ad hoc. But better looking.
MARTHA: I identified a pattern from UNIT's data on sudden deaths. Toxic shock. Nothing to link the victims. Different ages, sexes, ethnic origins, occupations. But there was a statistically significant concentration in South Wales.
JACK: Come on, Martha, be honest. You just came all this way to see me.
MARTHA: Still struggling to conquer your shyness, Jack?

And later on, in private, Martha and Jack have a conversation like this:

JACK: He must have thought he owed you a favour. Guess we all do. So Do you think you could get me one of those red caps for personal use? I’m thinking Ianto might look good in it.
MARTHA: You want uniforms, get your own. Now, am I going to get the guided tour?
JACK: Yes, ma'am, whatever you say, ma'am! Huah!

I got this dialogue from the transcript by the incomparable beccaelizabeth.