"But anyway, back to the album ... " This will prove the leitmotif of tonight's show, as the Roll Deep collective find themselves yo-yoing between two distinct worlds. In one they are wannabe pop stars signed to the same EMI subsidiary as Joss Stone, on stage to promote their latest fun product and shift some units. In the other, they are lynchpins of the underground grime scene, fast-flowing MCs who spit subversive words at the speed of light and answer to nobody. The problem is that both of these worlds are real.

Yet that juxtaposition also creates magic, and tonight's show contains many flashes of brilliance in both camps. The crowd joins in with the catchy salsa-infused chorus of their next single, Shake a Leg, which is all about dancing with your grandma, and then watches in awe as founding father Wiley takes to the mic, or while special guest Skepta raps about being a "a bad boy from Nigeria".

Roll Deep are pop enough to bring in guest female vocalist Alex Mills for some garagey melodies, but battle-scarred enough to freestyle through the technical hitches that keep threatening to bring the show to a halt. They're a hard-working bunch, constantly reaffirming their commitment to "grafting", and there are enough of them on the stage to form a football team, with subs being brought in from the bench throughout.

While their true skills are a pleasure to see, it's all the more disheartening to realise the compromise they've made on their major label releases. They get halfway through recent single Heartbreak Avenue, based on a Motown-sounding song by the Maisonettes, before interrupting themselves to say, "That's the commercial business. We got a little remix of that tune," and ditching the singalong backing track to rap harder, faster and better over some impressive beats. Not just rolling, but also deep.