Warren Ellis is on characteristically verbose form onstage at London's tiny Cargo, and this evening, the man known to his parents as Paul Hewson is the target of his withering ire. "This is a song about being reborn as a haemorrhoid in the arse of Bono vox from U2," he lances by way of introduction, before the Dirty Three launch into a song he informs the crowd is now titled 'I Was A Teenage Haemorrhoid'. "At school you might have read about Dante's Seven Circles of Hell, but that's nothing compared to the eighth ring of Bono vox from U2..." Hewson makes a second appearance later, in Ellis' preamble to a lovely rendition of 'The Restless Waves', a long and rambling story of post-fame retirement featuring Pauls Hewson, McCartney, Gadd (look him up) and Newman. "In the valley of the Pauls," deadpans Ellis, "it's fuckin' dark."

Such is always the way with the Dirty Three. Ellis, resplendent in shirt undone to the belly button and looking every inch the rogue, is a magnetic frontman. His skills as raconteur elevate the trio's gigs to unique events - his stories vary slightly in the telling every night, and his barbed asides nip any accusations of po-facedness in the bud; a combination all the more winning when paired with such eminently serious and sad music. While on the surface subverting his songs' sentiments at every turn, Ellis' physical representation of them - through story, yelps and screams, high kicks, crab-like dancing - serves instead to amplify their emotional intensity. It's one of the main reasons why, where so many of their instrumental folk/rock contemporaries have long sounded ready to be shipped off to the valley of the Pauls, Ellis, Mick Turner and Jim White continue to sound so vital, so forceful, so hungry. It's also a slightly damning trait, in that the trio's recorded output has never been able to live up to the elemental power of their live performances. This evening, as usual, they sound like a completely different band to the Dirty Three that played on this year's new album Toward The Low Sun.

In the live arena, even the group's most languid songs tear the senses ragged like barbed wire. Ellis' violin shreds high in the mix, ripping through its surroundings and serving as focal point: less instrument, closer to the contours of a well-worn human voice. On 'Some Summers They Drop Like Flies' (introduced as "a song about coming home and finding out that a load of people you know have dropped dead"), a loop pedal stacks a series of see-sawing motifs into a teetering pile of almost-harmonies that wrench at one another slightly, near drowning out Ellis' bandmates before collapsing in upon themselves.

Almost inevitably for the de facto mouthpiece of a band, attention and praise for the Dirty Three's live shows tends to focus squarely upon Ellis. But where he's particularly vital in the larger, late-night festival shows they more commonly play in the UK - acting as a point of access for casual listeners - the close settings of tonight's gig emphasise the equal importance of White and Turner's roles. Turner's guitar is almost a non-presence in the music, which is precisely its strength: sprinkling diffuse sprays of notes through the background, it lends depth, and provides an anchor when everything around it whips into a stormy frenzy. White's drumming, though, is little short of remarkable, and equally essential to the music's emotional resonance as Ellis' lyrical violin. His percussive backdrops are continually in motion, tossing and turning like waves on the sea (it's little coincidence that an early album was titled Ocean Songs), building to miniature crescendoes before ebbing away just as fast. We're left with the sense that White's drums tap into the rhythms of nature, both gentle - evoking as they do the movement of water and the rustling of trees in the wind - and violent: the sudden thump of a prone body to the ground.

That's the reason why tonight's gig, for all its triumphs, feels so unexpectedly muted. Festival shows and performances outside in particular tend to rob bands of the benefits of an intimate setting. However, in the Dirty Three's case they actually intensify its wildness and emphasise its concern for the untamed world, allowing each player's instrument space to breathe in the mix, and allowing each moment to be modified slightly by drizzle or shifts in wind direction. The Cargo, a tiny basement-ish space, crams all three instruments into wall of noise that tends to stifle each individual's performance. As a result, the gig frequently ambles rather than soars. Thankfully, a begged-for encore of 'Sue's Last Ride', a song that plays both to the spacious and firey sides of their oeuvure, serves as a monumental closer, its several distinct sections drawing focus to each player in turn. At its peak they pause for a few long seconds, building tension, before Ellis leaps into the air and they finish with a triumphant flourish.

"... And remember...," waves Ellis to the crowd as he introduces their final song, before faltering, forgetting what he'd planned to say next.

"Remember what?", comes the catty retort from someone in the crowd.

Ellis grins and shrugs. "Just remember."

Photograph by Valerio Berdini, taken at ATP's I'll Be Your Mirror at Alexandra Palace