- Anti-Villain: They may be delinquents but they are loyal to each other, and trying to cope in an impoverished reality.
- Delinquent: When your introduction is basically "a gang of teen muggers decide to pick on a nurse on Bonfire Night", you've hit this trope. Deconstructed, though: given their various backgrounds, they don't have many other readily available options. The more the film goes on, the more humanisation for the audience they get.
- Don't Tell Mama: A common theme with those who have family who care. "Playing video games at a mate's..."
- Five-Man Band
- The Hero - Moses - The clear leader of the group.
- The Lancer- Pest - He gives Moses a lot of support.
- The Big Guy- Dennis - The most hotheaded of the group.
- The Smart Guy- Jerome - Probably the most level-headed one - and he has glasses.
- The Chick - Biggz... well he does spend half the movie hiding in a dumpster.
- Hidden Depths: All of them, even the tag-alongs Probz & Mayhem, have surprising levels of expertise and characterization hidden within some of the daft stuff they say and pull.
- The Yardies: Or, at least, the kids of Yardies and apt to take up the trade. These guys are third or fourth generation, but still stuck in Estate life.
A quiet teenage gang leader and orphan looking for respect around the Block.
- Anti-Hero: Moses is a low-level criminal and mugger on the verge of becoming a drug dealer but he's also a brave, loyal person in a difficult place in life.
- Badass Biker: Moses is the only one who doesn't crash his bike at any point.
- Held Gaze: Dude rocks this as a whole communication style.
- Heroes Prefer Swords: Played with: he falls in love with that katana at first sight. But, it takes a lot of trial-and-error learning (with steep consequences) to use it in close confines and he gets called out on picking it, to boot.
- Hidden Depths: Much of the film revolves around the fact that there's more to Moses and his friends than meets the eye. Moses might be a low-ranking mugger, but he has a sense of honor and a difficult home life.
- Implied Love Interest: Moses and Tia seem to hold some romantic interest in each other.
- Katanas Are Just Better: He uses a katana for the majority of the film; it belongs to Dennis, but he loans it to Moses.
- Nice Job Breaking It, Hero!: Downplayed. Moses kills the first alien, and by doing so calls the rest of the aliens down upon him and his friends. It leads to a number of deaths, but he could hardly be blamed for failing to guess the mating habits of extraterrestrial life. In fact, if he hadn't killed the first alien, things would have been a lot worse. The aliens would have mated with the queen and bred en masse, allowing them to invade the entire city.
- The Not-Love Interest: To Sam, and her to him.
- Oh, Crap!: His expression screams this when he lodges his sword in the wall by accident, during a confrontation with an alien.
- Perpetual Frowner: One of the reasons why his actual age comes as a surprise.
- Red Oni, Blue Oni: He's the blue to Dennis's red.
- Scary Black Man: He tries to play this up a little, for the sake of intimidation.
- The Stoic: Moses' default expression seems to be a resting scowl, which can be attributed to him trying to play up an intimidating image.
- Standardized Leader: He often comes off as this.
- Younger Than They Look: You'd swear blind that he must be between eighteen and twenty by both the way he looks and acts. NOPE.
Moses' smart aleck second-in-command of the gang.
- Batter Up!: Uses an aluminum bat as his backup weapon.
- Buffy Speak: You can thank him for coining the term Big alien gorilla-wolf motherfuckers to describe the aliens.
- Deadpan Snarker: The most sarcastic of the group.
- Fatal Fireworks: Uses fireworks as his main weapon.
A hotheaded pizza delivery boy and member of the gang.
- The Big Guy
- Big Guy Fatality Syndrome: Hes the first of the gang to die.
- Car Fu: Uses a police van to kill one of the aliens.
- Hot-Blooded: He's easily the most aggressive and quick to anger out of the gang.
- Off with His Head!:One of the aliens bites down onto his helmeted head and rips it clean off, sending it bouncing off the walls.
- Oh, Crap!: When he realizes that the gun he took from the kids is just a realistic looking toy. The aliens subsequently kill him.
- Red Oni, Blue Oni: He's the red to Moses's blue.
- Token Evil Teammate: He's the most unpleasant gang member and is perfectly willing to leave Sam to die because he views her as an annoyance.
A schoolboy and member of the gang.
- Character Death: Killed by the aliens on Floor 19.
- Machete Mayhem: Picks up a machete as his weapon.
- Nerd Glasses: He wears a thick pair of glasses.
- Only Sane Man: He's often the voice of reason and the most level-headed in the gang.
- The Smart Guy
- Token Good Teammate: Not that the rest of the gang are evil, but out of them all Jerome is the most blatantly likable and even-tempered members. He sympathizes with Sam and certainly doesn't enjoy the mugging, even less so than the other members.
The youngest member of the gang.
Other Block Residents
Samantha "Sam" Adams
A nurse and new resident of the Block.
- Deadpan Snarker: She has a subtle wit exasperated by the...'challenging' circumstances.
- Held Gaze: Frequently with Moses.
- The Medic: She's a recently graduated nurse.
- The Not-Love Interest: A key dynamic of the film is her relationship with Moses, but it's never romantic. It's a gradual development of understanding, respect and friendship after an initial antagonistic encounter.
- What the Hell, Hero?: She delivers one to Moses and the gang.
The local weed dealer who lives in the penthouse of the Block and knows everyone.
- The Stoner: Well, he does deal weed. It's a professional side effect.
Ron's feared boss and the local psychotic gangster of the Block.
- Asshole Victim: It's hard to mourn for Hi-Hatz when he's ripped apart by the aliens, considering he's a psychopathic killer.
- Ax-Crazy: Hi-Hatz is as bloodthirsty as the aliens; he swings from mood to mood, kills when he feels like it and pulls out his gun at the slightest provocation. He actually gets progressively worse as the night goes on.
- Big-Bad Ensemble: He's the main human antagonist.
- Drives Like Crazy: To the point where it's a wonder that he's alive in the first place.
- Establishing Character Moment: Introduced while singing along to a rap song about shooting a snitch.
- Faux Affably Evil: Extremely faux. Even Mayhem and Probz don't seem fooled by his friendly act, and just give him information to get him out of their hair.
- The Noseless: When the aliens kill him, there's a shot of his face sans nose.
- Only Known by Their Nickname: His real name isn't revealed; the Block knows him solely as Hi-Hatz.
- Skewed Priorities: Tries to shoot at the gang while the aliens are practically on top of him.
- X Treme Kool Letterz: It's right there in the name.
A resident of the Block.
- Action Girl: The girl is a serious badass; when aliens attack, she barely hesitates to attack right back.
- All Girls Want Bad Boys: Subverted; she's implied to have a crush on Moses, but is highly critical of his criminal lifestyle.
- Improvised Weapon: Picks up a lamp and breaks it to make a makeshift taser.
- Screw This, I'm Outta Here!: She, Dimples, and their friends flee the block when Dennis is killed.
- What the Hell, Hero?: She gives a few of these to Moses.
A resident of the Block.
- Improvised Weapon: Uses an ice skate to kill an alien.
Reginald & Gavin A.K.A. Probs & Mayhem
- Big Damn Heroes: They're responsible for rescuing Biggz from an alien who's trapped him in a dumpster.
- I Just Want to Be Badass: They naively aspire to be like Moses and his friends, who they see as tough gangsters. They do, however, get to be badass when they fight one of the aliens.
- Kill It with Fire: How they kill one of the aliens when Probs sprays it with petrol and Mayhem throws a flare at it, with inevitable results.
- Those Two Guys: They always appear together.
A student stoner and one of Ron's customers.
- Author Avatar: Joe Cornish has admitted that Brewis is his stand-in; a well-meaning but dorky and inept young stoner.
- Chekhov's Skill: Brewis' stoned intake of nature documentaries turns out to be quite useful with regards to theorizing on the nature of the aliens.
- Erudite Stoner: For the entirety of his screen-time he's at least semi-high, but no less coherent.
- Nice Job Breaking It, Hero!: Halfway down the hallway to Rons, Brewis panics and runs off, leaving Jerome behind. As a result, Jerome gets lost in the smoke and killed.
- Pretty Fly for a White Guy: He's introduced hilariously lip-synching to KRS-One. He later tries to bond with the Gang, but he's clearly a middle-class dork and they aren't impressed.
The main antagonists of the film, the unnamed Aliens are ferocious beasts that rain from the sky to wreak havoc on the Block and its inhabitants.
- Aliens in Cardiff: Gorilla-wolf motherfuckers in a South London slum.
- Bioluminescence Is Cool: They have glowing neon teeth.
- Bizarre Sexual Dimorphism: The first, small alien killed at the beginning is in fact a female, while the males are hulking, black ape-like beasts.
- Dark Is Evil: The aliens are black, so black that they seem to absorb all light and none of their external features can be easily seen, save for the neon-blue teeth.
- Dead Guy on Display: The first small alien, after being killed by the gang, is paraded around like a trophy by the boys, which backfires on them horribly later on.
- Eyeless Face: Both types of alien have no eyes, relying on echolocation and smell.
- Glass Cannon: Are powerful and aggressive creatures but individually are easily defeated, even by two teenage girls with only a blanket and an ice skate.
- Kick the Dog: One of them devours Dennis' dog offscreen.
- Kill It with Fire: Probs and Mayhem take down one of the beasts using a firecracker and a water gun full of gasoline, setting it on fire.
- Killer Gorilla: The male aliens are ape-like in appearance and covered in shaggy black fur, while the first small female alien resembles more like a hairless baboon.
- Lightning Bruiser: Are very fleet of foot, and can even outrun the boys on motorcycles!
- Made of Iron: One alien absorbs six bullets from Hi-Hatz and still manages to slaughter both of his companions.
- More Teeth than the Osmond Family: And they glow in the dark!
- No Name Given: As the aliens were an unexpected arrival and are encountered by non-scientific crew, they are never formally given an official species name. The closest we get is Pest dubbing them "gorilla-wolf motherfuckers".
- Pint-Sized Powerhouse: Though it easily is killed by Moses and the gang, the first small alien manages to put up quite a fight and manages to wound Moses.
- Super-Persistent Predator: They chase down the boys through the block and manage to find them despite there being hundreds of rooms in the building! Turns out they were following the scent of the female alien that Moses killed.
- To Serve Man: Seem to have a taste for human flesh, though eating people isn't their primary objective for invading, but rather to mate with a female that signaled with a pheromone.
- Weaksauce Weakness: Turns out that the big black ones are males, and they simply can't resist the scent of a female (even a dead one) and such Moses exploits this to trap them all and kill them in a gas explosion.