Sunday night in Glasgow club The Garage. As the crowd whoops and roars, a man-mountain is hurled from a balcony, while another is tossed headfirst into the bar before being attacked by dustbins and a steel chair. The floor is slick with blood, beer and sweat, there’s glass everywhere, and yet the mood is oddly jubilant.

Welcome to Insane Championship Wrestling (ICW), a full-throttle blend of pantomime, club brawl, traditional grappling and high-octane soap opera, which has taken Scotland by storm and is now heading south. You can see what all the fuss is about on BBC3 tonight.

Scottish men knocking lumps out of each other is practically a national sport, but ICW takes it to the next level, or at least pretends to. As well as the carnage wrought indoors, bouts frequently spill out onto the streets, where burly blokes calling themselves Mikey Whiplash, Rampage Brown and Kid Fite throw each other against passing buses and advertising boards.

According to its creator, Mark Dallas, ICW is “theatre for a new generation” – with theatre being the operative word. Although it requires impressive degrees of physical skill and stamina, the violence of ICW is, in the best tradition of televised wrestling, strictly of the cartoon variety, delivered with a nod and a wink. Any sense of jeopardy is cooked up in order to entertain.

An amiable father of one, the 29-year-old Glaswegian is the brains rather than the brawn behind this operation. Dallas dreamt up ICW for disillusioned fans who felt that mainstream wrestling had become too tame. Taking the sport out of sedate community halls and into nightclubs, ICW serves it up with pumping music and lashings of booze, blood and profanity.

A going concern since 2009, Dallas knew ICW was going to work when one early show almost incited a riot. “The ring broke and everyone spilt out past the bouncers onto the street,” he says, during a rare lull at the troupe’s office/gym complex in central Glasgow. “Wolfgang threw Kid Fite against a bus. Someone else got chucked into the door of Cineworld. The security staff ran away. Two riot vans turned up. The next morning the phone went, and it’s a different club, wanting to bring in ICW. Our reputation was built on things like that.”

ICW created a cult following by posting videos online featuring not just fight footage but backstage drama concerning dastardly baddies (Wolfgang, BT Gunn), cheeky underdogs (Grado, The Wee Man) and hirsute heroes (Jack Jester, Drew Galloway). Dallas and his team concoct epic storylines for them all. “You can tell an amazing tale in a wrestling match,” he says. “People get emotionally attached.” The wrestlers are close friends outside the ropes, but inside the ring it’s an alternative reality of battling top dogs, good versus evil and professional vendettas.

The animosity might be contrived – as are the predetermined outcomes of each fight – but the pain is real. “Call it fake and the wrestlers get angry,” says Dallas, with a look that suggests you wouldn’t like ICW wrestlers when they’re angry. “A steel chair hitting you on the back of the head is a steel chair hitting you on the back of the head. That’s real. At its purest, wrestling is an amazing art form, like a stunt show done in a single four-hour take. I defy anyone to see our live shows and not be highly entertained. It’s like the three-ring circus: if you don’t like the lions, you’ll like the clowns.”

Anyone who saw the BBC’s 2014 documentary about ICW, Insane Fight Club, will recall that the clown prince is Grado, aka Graeme Stevely, who still lives with his mum and dad and lists his interests as “food and wrestling – in that order”. He bounced on stage to Madonna’s Like a Prayer, coined his own catchphrase – “It’s yersel’!” – and dyed his hair with supermarket food colouring. Far from your typical muscleman, Grado confesses he’s “one of the most unfit guys you’re likely to meet. I’m built like a loaf of bread”.

In this week’s follow-up documentary, Insane Fight Club II (already shown on BBC Scotland), Grado heads up a chaotic promotional road trip to England. He parades around Leeds city centre in his vest, doing a demented rain dance while haranguing Japanese tourists with a loud-hailer. Later, he undergoes hypnotherapy to curb his appalling eating habits (“I had a hot dog afterwards,” he tells me). ICW fans revere him, and they’re not alone. Grado now has a regular role in BBC Scotland soap River City.

A clown he may be, but Grado’s rough underdog charm lies at the heart of ICW’s appeal. These are men from all walks of life, most of whom still hold down day jobs, who have formed strong bonds and discovered a sense of purpose through wrestling. “I don’t pretend to be somebody I’m not,” says Grado. “People look at me and see the common man, the guy who loves a chippie and a drink. Then I go into the ring and give it my all, even when I’m terrified. I represent people who might not have the belief that they could do this.”

Dallas echoes those sentiments: “ICW provides some artistic fulfilment in my life, otherwise I’d go nuts. It sounds cheesy, but the moral of this story is not to worry about what other people think about you. Maybe you’re at school, you’re into ballet dancing and everyone’s laughing at you. Who cares? Be yourself, be different. At ICW, we all know who we are, and we say it proudly.”

It’s an expanding operation. Thus far, shows have mostly been confined to Glasgow, where ICW recently sold out the Barrowland Ballroom, the city’s legendary concert venue. Now England is being battered into submission. Since the second documentary was filmed last year, ICW has made two successful trips south. “Liverpool and Newcastle give the Glasgow crowd a run for their money,” says Grado. “People go nuts because they’ve seen the videos, they’ve seen the documentary, and now we’re bringing it to their town.”

Dallas’s ultimate goal is to have a regular ICW slot on British television. He’s already in talks with channels. “I’d love a weekly wrestling show with backstage content and location shots, so the stories away from the ring build interest in what’s happening inside it. I like the idea of it being like EastEnders, but every character is a wrestler and every week ends in a fight. Imagine Phil Mitchell in a singlet!” Now that really is scary.

Insane Fight Club review: "It puts you in a full nelson - funny, heartbreaking and compellingly violent"

Insane Fight Club II is on BBC3 tonight (Wednesday 1st July) at 10.00pm