A doubly impressive achievement this: the debut of writer-director Asante and lead actor James, it's also a film that makes no attempt to ingratiate its characters or subject matter with the audience. The ending - plainly prefigured in the opening scene - is as downbeat as may be imagined, yet the viewer is left in awe at the skill on show.
Set in a grimy neighbourhood of an unnamed South Wales city, it opens with a gut-wrenching and brutal street beating and tells its story in a long flashback that explains how it came about. James plays downtrodden solo mum Leigh-Anne, whose council flat home serves as a dope-smoking den for a trio of layabouts: Gavin (Jones), Robbie (Sheppeard) and Stephen (Wong), who spend their days harassing non-whites (all of whom they label Pakis).
Meanwhile, Leigh-Anne's limited mothering skills earn her endless nagging from a well-meaning grandmother (Blethyn).
Comparisons to Ken Loach and Mike Leigh are immediate - when welfare authorities ("the social") threaten to take Leigh-Anne's baby away we are reminded of Loach's harrowing Ladybird, Ladybird.
But you have to dig deep to detect the film-maker's sympathy for her subjects as she takes the brave step of inviting us to hate the people she depicts.
We can't help feeling for her as she gazes at Hassan (Haden), the "Paki" (actually Turkish) man across the street, whose loving relationship with his daughter underlines what is missing from her own life.
Her way of expressing her jealousy is shocking, and a way she has of making a little money on the side is closer to sickening.
Urban liberals may shrink from such an unvarnished approach, which does not unambiguously define its characters as a product of underprivilege and social injustice. But Asante, a black Londoner who grew up in a white neighbourhood with the National Front holding meetings at the end of the street, may be excused for wondering whether race hate can be excused by social circumstance. She has made a bleak and darkly brilliant film and announced herself as a bright new talent.
Cast: Stephanie James, Nathan Jones, Gary Sheppeard, Dean Wong, Sara Gregory, Oliver Haden, Brenda Blethyn
Director: Amma Asante
Running time: 90 mins
Rating: R16, contains violence, offensive language and sex scenes
Verdict: Grim but enormously confident feature debut unblinkingly anatomises life among working class Welsh no-hopers