The queue is stretching down Brixton Road, and in front of me there's Nicola Roberts of Girls Aloud, while members of The xx are among the excited crowd.
"Wow. Hi," says James Blake, as he emerges onto the stage and takes his pew behind keyboards and an amalgam of effects pedals. If 22-year-old Blake is overwhelmed by the sudden response to his music, that's hardly a surprise – most of the fans present tonight had bought tickets prior to his December show at the same venue, while his album is not out until February. Such is the hype that industry awards such as the Brits Critics' Choice and BBC Sound of 2011 poll can bring; Blake was last month revealed as the runner-up to Jessie J in both. But it's his live performance that will cement his status as one of the artists to watch this year.
Controlled and composed, the electronic composer and graduate of Goldsmiths College begins his short set accompanied just by synth. His second song, "Wilhelms Scream", is named after a sound effect used in films from the 1950s. If the title has become a cliché, Blake's track is anything but. Letting his soulful and plaintive vocals lead the way, he builds layers of keys, sound effects, picked guitar and complex beats with the help of his bandmates – schoolfriends Rob McAndrews on guitar and sampler and Ben Assiter on percussion – until his vocals are almost drowned in the echoing sound effects, giving resonance to the lyric "I'm falling" as the claustrophobia sends ripples of shivers through the audience. Then his vocals surface, and the tension breaks. It's these kind of dynamics that Blake employs in his electronic music that are so powerful and compelling.
In "I Never Learnt to Share", as in "Lindesfarne", he records and loops his vocals on a three- or four-part harmony to tremendous effect, his fingers moving fast over the keys; but it's here that the songwriting doesn't feel quite as complete as its performance. His vocals have the vulnerable emotive pull of Bon Iver.
Like The xx, on their distinctly urban-feeling debut album, Blake makes use of the space in music rather than filling every moment with as much noise as possible. Every sound is measured and contributes to the atmosphere of his impressive songs – the perfectly pitched electronic snare, for example, on "Wilhelms Scream". Alongside his peers Jamie Woon, Katy B and Darkstar, Blake is part of a new lease of life for dubstep – but it's the latter who creates as much emotion through his music as Bon Iver, while having the capacity to make the crowd dance at the same time.
It is "Limit to Your Love", his Feist cover, that first garnered Blake attention, and it duly draws the biggest applause of the night.
At the end of a mesmerising set, he further endears himself to his fans by modestly applauding the efforts of his support act. "Thank you so much for coming out. Really. I've never played a gig like this so I will remember this for a long time." I shouldn't think he'll be able to. The next one will be even bigger and more memorable, and the one after that.