This double bill was the first event in the current Brit jazz festival to sell out, and it didn't disappoint. Everyone lucky enough to witness it must have come away reeling at the sheer quality and quantity of music made by these young British bands. Kairos are carving out their own niche of airy European chamber jazz, while Beats & Pieces are a brash 14-strong band from Manchester, playing material by the precocious Ben Cottrell. Both are packed with great performers who foreground the material, and singer Emilia Mårtensson made an elegant cameo appearance with each band's set.

The acclaimed Kairos 4tet are led by composer-saxophonist Adam Waldman, who looks like a downbeat 1970s star in Afro, medallion and waistcoat. His compositions create distinct musical atmospheres within seconds: they're not like conventional jazz "heads", but closer to classical studies, with a touch of the chiming, swirling epics of Esbjörn Svensson, or the folky tunefulness of Portico Quartet.

Beats & Pieces reminded us that jazz can be pleasingly vulgar, too. Shouty ensemble sections in tunes such as Bake, Queen Spark and Jazzwalk (inspired by the Street of Fame in Burghausen, where the band won the 2011 European Young Artists' jazz award) shook Ronnie's to its low rafters, with kick-ass solos from all its players, including trumpeter Nick Walters, guitarist Anton Hunter and tenor saxophonist Ben Watte.

But there are plenty of jazzers who can play brilliant solos. Few bands play work of this complexity with such passionate conviction. It was inspiring to hear them build from delicate, barely detectable ensemble textures via hammering riffs to full-on freak-outs, never dropping a beat.

Cottrell introduced a brace of Radiohead covers by mentioning the inspiration of the Colin Towns Mask Orchestra at Ronnie's last summer. Movers and shakers such as Towns, Matthew Herbert, Darcy James Argue and Cottrell demonstrate that large ensembles remain a vital force in contemporary jazz.