In the smoke-filled basement of Bristol’s Brunswick Club, the T-shirts are off for Giant Swan. The duo coax unearthly noise from a web of drum machines and guitar effects pedals; as Robin Stewart’s robotic howls and Harry Wright’s clattering beats resolve into techno, their audience of peers in Bristol’s music community disrobe from the sweat and explode into dance.

For the family of artists in the room, in January 2018 at the last festival by Howling Owl Records, this closing show marks the start of a new chapter – one that has been moving into the spotlight ever since.

Several breakthrough artists are now creating a vibrant new Bristolian underground, a scene long obscured by the enduring legacy of the city’s trip-hop era, when artists including Massive Attack, Portishead and Tricky created pre-millennial tension by splicing dub and hip-hop. Like those trip-hoppers before them, many of the new avant gardists are rooted in the city’s vital reggae soundsystem culture, but what marks them out is an impulse to marry it with the theatrical world of guitar music.

At their forefront is Giant Swan. Nodding to both noise-rock and techno in their recently released self-titled debut album, a work of soaring imagination, Wright hopes that “what we’re doing, and what our friends are doing, is helping to blur that line”.

I meet the duo at The Old Bell near their Bristol studio, currently in use by the astonishing avant-pop artist EBU, who appears in a portrait on their album cover. Elsewhere in the pub is Ky Witney, drummer in Wright and Stewart’s art-rock band the Naturals. It was while trying to use their pedalboards to devise more electronic sounds for this band that the two guitarists started Giant Swan as a drone project. Their dance leanings began when Wright broke his arm before a gig, swapping his guitar for a friend’s drum machine, but they had already become infatuated with Bristol’s dub nights. “There was this eureka moment,” Stewart claims, in “hearing sound systems take on this role of being grimmer and heavier than the craziest guitar band ever.”

By blurring this distinction, Giant Swan hope to be inclusive to listeners from both worlds, “conversing” with their audiences by improvising in the democratic space of the dancefloor. “We’re hearing it for the first time too, so we’re all in this together,” Wright says with a grin. “If it doesn’t sound good, we know!” Stewart views Giant Swan within a wider Bristol impulse to “go to the most extreme point we can think of,” which has developed over the past 10-or-so years. “Before that, Bristol was quite a dark place musically.”

The 2010s opened with the confluence of two events. The subversive label Howling Owl arrived, and – after an argument with a promoter – was blackballed from holding gigs at any local venues. Their consequent shows in non-venues (crypts, Scout huts, art galleries) not only rewired Bristol’s live circuit and label culture, but drew together a community of previously isolated new artists such as the Naturals, Spectres and Idles. Around this time, a circle of Bristol avant gardists collectivised to form the shadowy and highly productive Young Echo; spawning several labels, a radio show and a vast body of recordings, their sonic and entrepreneurial extremity inspired a new wave of labels, promoters and artists. Having been at their first bedroom transmissions, Wright says Giant Swan are indebted to them for advice and inspiration: “Young Echo proved you can build this community out of experimentation, or a sense of otherness.”

Bad Tracking performing live. Photograph: Simon Holliday

The latest manifestation of this spirit is Avon Terror Corps, a “crew label” rejecting nostalgic perceptions of “the Bristol sound” to promote the city’s subversive new music. Ranging from goth duo Fever 103 to “cyborg industrial trap” artists Kinlaw & Franco Franco, this colourful circle’s prime mover is Miles Opland, creator of leftfield dub label Bokeh Versions.

Opland is moving flat when I visit him, packing up gig posters, records and memorabilia from his years in Bristol’s music scene. “What relics do we have here?” he asks himself with a smile, before pointing to the poster for the first Bokeh Versions night. This featured the live debut of dub producer Sunun, whose work forgoes computers in favour of live vocals and real instrumentation. “There’s no one doing what she’s doing with a mixing desk,” he says. “She is a band, for want of a better term.” Opland has an eccentric fondness for spreading misinformation: one poster claims that thrash metallers Napalm Death are appearing, while on that debut show’s anniversary, he put the old posters back up around town. “I wonder if anyone turned up… ”

Avon Terror Corps formed as a reaction to the closure of Bristol music hub The Surrey Vaults. “DJ October once told me it’s the closest thing we could have had to CBGBs,” Opland says. When it closed in 2017 at a week’s notice, “we drank it dry and took any furnishings we could – that weird pot is from there,” he continues, pointing to an enormous vase behind me. ATC was formed by the “misfits and weirdos” who coalesced there, and has already produced several critically lauded records. He plays me some new music from the duo Bad Tracking, pairing spoken word with industrial noise played on old cassette machines, and themed around the body’s relationship with technology. Giant Swan’s Robin Stewart claims their devastating live sets, which see their nude vocalist choke himself with a belt, often bring him to tears.

Opland baulks at the mention of trip-hop, saying nostalgic media coverage of that scene has obscured the city’s new music. “I know for a fact we’re going through a golden age right now,” he says. “Robin said to me about 18 months ago that something’s happening, or about to happen. I don’t mean we’re about to sell a million records – I mean we’re about to do all the stuff that’s going to mean something to us when we die,” he says softly, looking at the posters again. “It’s the most exciting thing I’ve ever felt.”

‘A sonic Guernica’ … Harrga. Photograph: Simon Holliday

Another of ATC’s affiliates is Harrga, whose album Héroïques Animaux de la Misère channels Bristol’s experimental impulse into urgent political music. Over Miguel Prado’s abstract electronic compositions, Dali De Saint Paul’s multilingual lyrics in French, Darija and more present a harrowing exploration of the refugee crisis. The album has been termed – she explains in the pool room of The Old England – “a sonic Guernica.”

As in Bad Tracking or Giant Swan, Harrga’s cross-pollination of punk elements with beat-driven electronics has a conceptual foundation. Album-opener Melilla is named after a Spanish autonomous city in Morocco, frequently used by refugees fleeing war zones to access Europe; to do so, they must vault two walls covered in razor wire while evading police patrols. The shouting that opens the song, Prado explains, “is a field recording of the moment they are able to trespass into the city”. The middle sees De Saint Paul repeatedly shout “bosa” (Bambara for victory), which is called out by successful crossers. The end, segueing into a dance-oriented beat, was inspired by trap music made in Andalusia by second-generation Moroccan migrants – overall, it evokes refugees entering Europe and suffusing it with new art.

De Saint Paul recalls her first experience of St Paul’s Carnival here; seeing “all these people joining in the streets, dancing to these really loud beats,” she felt an openness she considers foundational to Bristol’s experimental scene. “These people from Avon Terror Corps or Young Echo are trying to push boundaries, but they share this idea of making music to make people share in the community. If you go to Giant Swan, you can’t stay like this!” she laughs, stiffening her arms by her sides.

Cross-pollination … Scalping. Photograph: Rowan Allen

The weekend we meet also sees the closing-down night at local venue Start the Bus (later Hy Brasil Music Club). Half of Bristol’s music community convenes for a final blowout, spilling into the upstairs offices and throwing feathers from the balcony, presumably left from when those rooms belonged to Howling Owl Records. “This is really sad,” says Alex Hill of Scalping, having once seen music here as often as four times a week. Among my own memories of the venue is Scalping’s first gig. Gaining attention for their extraordinary shows and acclaimed EP Chamber, they are now set to become Bristol’s next national breakthrough.

I visit Scalping at Pirate Studios, where the four-piece are practising for a tour with Mercury-prize nominated Black Midi. The latest example of Bristol’s cross-pollinating impulse, they use the setup of a traditional guitar band to create live techno drawing from post-rock and industrial; flickering in the pitch-black room, a projection screen accompanies their set with Technicolor animations. “This band wouldn’t exist without Giant Swan,” bassist James Rushforth says, having co-organised the gig where the Giant Swan first used a drum machine and “everything changed. It was so good that Logos, the main headliner, gave us back his fee.”

This family of experimentalists in Bristol is bound by a wild love of extremity, and the inspiration they continually draw from each other. Shrugging off the millstone of trip-hop, they are creating not only the country’s most bewilderingly forward-thinking music, but proof of the strength found in community, one that’s “more important than your family, where you grew up, where you’re from,” says Opland. “You can rise above your current situation by seeking the people you can make real change with.”