Now here's a movie that could really use an exclamation point in the title: Attack the Block! But no.
This is a tongue-in-cheek alien horror flick. Dropping—literally—into London are dozens of unpleasant beasties, about the size of grizzlies with blue-glowing teeth. But for some reason, their ground zero is an area parasitized by young lawless thugs. While the gang is mugging Samantha, a plucky young nurse, one of the beasts lands nearby, and proves no match for the gangleader Moses. But this initial victory proves to be just the opening battle, as the creatures proceed to seek vengeance against Moses and any other humans that get in their way. Samantha finds herself in an odd alliance with the bunch that accosted her earlier; will they prevail against their common enemy? Well, probably. But not without a lot of (as the MPAA puts it) "creature violence, drug content and pervasive language."
For a spacefaring race, the aliens don't seem very smart, and their goals are uncertain. If their goal is world domination, mixing it up with a gang doesn't seem like good tactics. But that's a quibble; it's probably not supposed to make much sense.