LONDON—In a country where the combined ethnic population represents a tiny 8 percent, young black music fans have rarely been the focus of popular-music marketing. But these days, black British DJs, label owners, producers and singer/songwriters are being hailed as the voice of the next generation. In fact, it can be argued that young black…

LONDON—This city’s been long-known as a multicultural haven, a world capital boasting a bustling population of brown and black Brits. But there’s a sad truth here, one that’s been growing in intensity: Most of London’s young people of color are more likely than not to know someone whose life has been literally cut down by…