Firing the starting gun on festival season, this annual all-dayer is an essential muster point for the art-punks, urban folkies and indie dads of South London. Local bands, breweries and venues are well represented: one of the stages is hosted by beloved Brixton dive The Windmill, and Black Country, New Road are among several acts appearing today who were hothoused within its reassuringly manky walls.

Anticipation for their set is high judging by the group of fans careening across the site early in the afternoon chanting the “BC,NR friends forever” refrain that kicks off the band’s new Live At Bush Hall release. But while that recording found the band coping admirably with the departure of ex-frontman Isaac Wood, today they don’t sound quite so assured. The idea of sharing the lead vocals around is in keeping with their all-for-one outlook, though inevitably it means they lack a focal point. The band’s well-crafted new songs boast more conventional appeal, at the expense of some of their former edge. BC,NR remain an intriguing enigma.

As such, they don’t manage to capitalise on the plentiful good vibes spread by the band immediately preceding them. Sunset Rollercoaster are five eager young chaps from Taipei who play immaculate, jazzy drivetime pop with nods to Haruomi Hosono and the first Phoenix album. It might be kitsch if it weren’t so sincere; Kuo-Hung Tseng’s voice contains a strong hint of melancholy, embodying the heartache in every dream home. Top marks, too, for their pitch-perfect version of Dmitri Shostakovich’s “Waltz No 2” AKA the theme from Eyes Wide Shut.

Alex G draws one of the biggest crowds of the day to the main stage for his next-gen slacker rock. With nine albums under his belt, he’s certainly amassed a decent arsenal of tunes, although he’s not the most effusive of performers. But even if his unassuming delivery is kind of the point, it’s a thrill when he invites headliner Caroline Polachek up to perform “Mission”. There are some nice Mascis-lite solos too, but overall his set could with some more of the chaos that comes easily to Stockholm punks Viagra Boys.

Saxophone blaring, theirs is a pleasingly old-school racket reminiscent of X-Ray Spex and Rocket From The Crypt. Shirtless singer Sebastian Murphy has a tattooed paunch to rival any Newcastle United ultra, a feature that you (unfortunately) can’t ignore when he starts doing exercise moves around the stage. It’s not big or clever, but it certainly rouses the rabble.

However, they can’t hope to match the intensity of the Osees. Twin drummers flailing, John Dwyer’s merry men go from nought to sixty in the blink of an eye and never let up. Dwyer himself is a puckish master of ceremonies, dressed for the beach, guitar strapped just beneath his chin, occasionally prodding a toy keyboard. When they’re done mangling the corpse of heavy psychedelic rock, they manage to locate an even higher gear and start on hardcore punk.

If there’s one caveat, it’s that Osees carry no passengers. You’re either 100 per cent in or 100 per cent out; there’s nothing really to draw in the casuals, unless you count synthy new single “Intercepted Message” – and any crowd trying to sing along to its robust anti-royalist refrain is likely to be instantly kettled by the Met police.

Wide Awake evidently struggled to pull in a high-wattage headliner in the vein of Primal Scream last year. As it turns out, the festival’s biggest star played right at the start of the afternoon. You might not imagine the rarified aural balm of Arooj Aftab’s Vulture Prince as natural festival fodder, but this is a singer who can elevate your soul at a thousand paces before immediately pulling you back to earth with a withering New York put-down. She may be amusingly disparaging about the “techno shit” bleeding across from another stage but she’s also developed a way to combat it. Instead of the acoustic bass and harp format she toured with last year, she’s now playing with a guitarist who can do biting as well as gentle, and together with right-hand man Shazad Ismaily on electronics, they summon a stunning new maelstrom of noise in the middle of “Saans Lo”.

During a glorious closing “Mohabbat”, Aftab throws roses out to the front row, even as she jokes that her “poor upper body strength” means that she might struggle to get them over the barrier. It’s the consummate work of an all-round-entertainer, Liza Minelli sings the music of the spheres. Catch her this summer if you get the chance.