But this isn't the sound of the crushing epics of the Manic Street Preachers, or the wall-of-sound pop of Phil Spector, it's the ramshackle chic of street urchins, stumbling on to instruments and delighting in the sweet racket they make. And it's a fantastic brew; because while they exude the air of lucky amateurs it's a concoction that only the stony-hearted could resist.
They make a fist of the first song, pushing their lackadaisical habits to the brink of disaster, but they recover and stumble brilliantly from one breathless song to the next. Each one unfurling like a funny and melancholic Alan Bennett Play For Today compressed into five minutes. They will never rock the house but the songs from their new EP, Lazy Line Painter Jane, shine with all the drama and clumsy emotion of your first kiss.
During one particularly lengthy tune-up, the guitarist calls for requests and performs an impromptu solo version of Dylan's "Like a Rolling Stone", but even this is brilliant, with Dylan's original vitriol replaced with head-shaking regret.
At one point, as everyone is enjoying the spectacle of Belle and Sebastian in a church, a lone, crazed dancer suddenly and without reason starts flailing around like he's at a techno club and we all shuffle with embarrassment. Because that's how fans of Belle and Sebastian suffer life, with shuffling embarrassment, stolen looks, long lonely sighs and scribbled poetry. The audience look as if they've been hibernating since the Smiths split up a decade ago and there's even - horror of horrors - grown men in T-shirts and cardigan ensembles again. For one glorious night, the arrogant anthemic indie bands are thankfully a world away as people in a chapel in Islington gleefully worship at the altar of shyness and coyness. Amen.