With Margins Music, Dan “Dusk” Frampton and Martin “Blackdown” Clark join a long lineage of artists who’ve let the world know how London gets down. From London Posse’s “London Posse” to Tek 9’s “A London Sumting” to neighborhood-celebrating dubstep and grime cuts (Burial’s “South London Boroughs, Wiley’s “Bow E3”), the British urban underground has a tradition of proudly and defiantly associating its music with the place it was made.