The scene is a ballroom somewhere in Belgium. Couples are dancing, in a rather formal, old-fashioned way. The record they are dancing to is a Bill Haley single called Chick Safari. But this isn't a rock'n'roll revival night, nor is it a scene from a David Lynch movie. The DJ plays Eartha Kitt, the Skatalites, something that sounds like a northern soul record at the wrong speed. The atmosphere is friendly but exclusive, and the musical mood dark and opulent. This is a Belgian Popcorn club.

Popcorn is possibly the last truly underground music scene in Europe, one that has yet to be ransacked and reduced by adverts for Orange or KFC. Its narrative was formed by Belgians in the 1970s, largely from American records made in the 50s and 60s. It took its name from a club named in honour of James Brown's 1968 hit Mother Popcorn, but it has little to do with funk. The rhythm of a Popcorn floorfiller has to suit the unusual "slow swing" dance favoured by the Belgians; it could be Peggy Lee's sensuous Sweetheart, Hank Levine's filmic Image, Billy Storm's tormented teen ballad Easy Chair, or an early Tamla Motown single such as Little Iva's Continental Strut.

House DJ Eddy de Clercq started going to Popcorn clubs as a teenager in the early 70s, where he saw "couples jiving together in the most complicated steps and whirls. A mid-tempo slow jive, not acrobatic like in rock'n'roll, but very stylishly done, with the men leading the girls, or sometimes leading other men. Club Popcorn was also the first big club where gay people could dance together in public without being hassled. It was a very liberated, open and friendly kind of place."

Club Popcorn had started its life in a converted farmhouse 10 miles west of Antwerp, holding dance contests on Sunday afternoons. By 1971, it had extended into the farm's outbuildings and barns, and close to 3,000 people crammed themselves in every Sunday to hear DJ Gibbe Govaert's sets. "The streets were filled with parked cars and well-dressed punters all heading to this farm in the middle of nowhere," remembers De Clercq. "The main dancefloor was located in the old barn, surrounded by bars and elevated dance stages. It was so packed there was hardly any room to move. People were dancing on the bars, behind the bars and even on the cars parked outside. The atmosphere was so exciting, people started cheering and throwing fountains of beer once a popular tune came on. Sometimes people stage-dived into the crowd or started stripping to the music. The sound was unique, it was instantly recognisable, and very decadent to me."

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Popcorn's obscurity in Britain largely stems from our snobbish, long-held mistrust of European music scenes. "People really do have the wrong idea about Belgium," says Bill Brewster, the author of Last Night a DJ Saved My Life. "Musically, it's been far more innovative than people give it credit for, possibly due to the push and pull of the Flemish and French split." The writer Harry Pearson has described Belgium as having a "Mediterranean attitude in a northern European country", or "sex in duffel coats" if you will. The world of Popcorn, likewise, is an odd mix of sensuous music and beer-sodden dancefloors.

Popcorn has a very similar timeline to northern soul: it started as a regional phenomenon in the 60s and peaked commercially in the 70s before going back underground in the 80s. The main difference between the scenes was the tempo of the records, with Popcorn crowds needing records with a drowsy feel; DJs even played 45rpm singles at 33rpm to obtain the requisite atmosphere. "It was driven by beer rather than amphetamines," says Brewster. "But culturally Popcorn and northern soul were very similar."

In the summer, the scene would move en masse to Ostend, Belgium's equivalent to Blackpool. DJ Freddy Cousaert played at the Groove, a late night downstairs bar frequented by US marines, tourists and prostitutes – it was Cousaert who later looked after Marvin Gaye during his 80s sojourn in Ostend. The music he played at the Groove included ska, Latin jazz and even Broadway songs such as Stranger in Paradise, or Whatever Lola Wants from Damn Yankees – in the hands of Cousaert or other pioneering DJs such as Gibbe Govaert and Jeff Callebaut, this odd menu made sense. Ostend also had a club called the Versailles, which had direct access to the beach, leading sweaty clubbers to run drunk and naked into the North sea.

As Popcorn's popularity spread from Antwerp and across Belgium, the musical menu became wider. Younger DJs came out of the French side of the country and from the sizeable Italian community; by the mid-70s, early-60s British stars such as Kenny Lynch and Craig Douglas were being played alongside the R&B and ska, as were Italian crooners and milky US teen idols. For hardcore fans such as Eddy de Clercq, this was the same as kids dancing to the Joe 90 theme at Wigan Casino. EMI released a Popcorn Oldies compilation and the scene exploded. Pretty soon, Popcorn even had cash-in bands such as the dreadful Lou and the Hollywood Bananas who had hits in 1979 with Kingston Kingston and Hong Kong Ska. Now it had its equivalent to Showaddywaddy, it was time for Popcorn to go back underground.

The London DJ Niamh Lynch "first heard the term 'Popcorn' at a mod club called Shotgun in south London in the early noughties. Barbara Redd's I'll Be All Alone was played, and I loved it. I already loved rhythm and blues but this had a smoother, less choppy feel to it." Intrigued, she soon made her way to "a dedicated old-fashioned Belgian Popcorn club" in the small town of La Louvière. "They knew we were coming as I'd emailed ahead and they did everything to make us welcome. They actively asked for requests, played everything we wanted to hear, and looked at us like we were nuts when we did our normal-to-us dancing." While there has never been a dedicated Popcorn club in Britain, the sound began to work its way into soul nights in the noughties, at places such as Flipside in Dewsbury which would have a Popcorn special once a year, bringing DJs over from Belgium. Of the UK's current soul nights, the excellent Kingpin in Sheffield, also plays a smattering of stuff at the saltier end of the Belgian palate.

A trip to Belgium, though, shows a scene mostly populated by people over 40. Popcorn's sustainability, as with every musical subgenre, is down to the internet, which has opened the scene up to outsiders – there are now Popcorn nights and weekenders in Italy, Germany and the United States. As the Belgian clubs have no dress code and the music has few hard and fast rules, this has tended to jar with the British trainspotter mentality. Though British mods may favour its gritty R&B spins, these are only a small part of what makes it special; the purity of Belgian Popcorn is its very impurity. R&B, Broadway numbers, tangos, Phil Spector-esque girl groups and loungey instrumentals, they are all constituent parts of a rare, and still largely undiscovered scene. It won't stay that way forever.