The event, part of the SBC's Blitz festival, which runs until Sunday, featured workshops and performances celebrating both the established and more progressive strands of Irish dancing. An estimated 1,000 enthusiasts attended, many from overseas - including visitors from Slovakia, France and Spain - as well, of course, as a substantial Irish contingent.
Yet, until recently, the organisers of Blitz would probably not even have considered putting on such a day, let alone imagined that it could prove such a crowd-puller. Irish dance used to have a serious image problem. Expressionless, humourless, sexless - it scored perfect sixes on every count.
But that was before Riverdance. Amid all the nil points and cheesy beats of the 1994 Eurovision Song Contest, something much more significant launched itself before a global audience of 300 million. When the lord of the dance himself, Michael Flatley, exploded on to the stage, arms flailing, it was as momentous in its own way as William Webb Ellis's decision to pick up the ball and run.
Three years later, the beat goes on, and despite the widely reported rift between Flatley and his co-revivalists, both traditionalists and modernisers in the industry continue to bask in Riverdance's glow.
Moira Clerkin, organiser of Down By the Riverdance and co-founder of Clerkinworks, has no doubt about Riverdance's impact on public perceptions. "It has had great influence in terms of profile," she says. "People now know how skilful our dancing is and don't think of it as some fringe, folk, weird, backward thing. The Irish dancing world hadn't been prepared to step out and look at itself until, it has to be said, Michael Flatley and Moya Doherty saw its theatrical potential and realised it could go on a world stage."
For Linda Fryday, who runs dance schools in Dartford and south-east London, Riverdance has opened up new doors for her pupils. "Before, Irish dancing came to a standstill when the girls got to about 17 - they either gave it up or became teachers. Now there's such a great demand from follow- ups to Riverdance that they can work towards auditions. It's wonderful."
John Brooks is also a teacher, as well as a competition judge. His son Ciaran is currently touring with Riverdance. Brooks reports a surge of interest in Irish dancing from people of all ages. "I get hundreds of phone calls, in particular wanting to know where there are adult classes," he says. "Certainly, every teacher I know is getting a lot more enquiries. As well as encouraging a lot of young people to start, Riverdance has also brought people back in who drifted away when they were 12 and 13."
Brooks confirms the knock-on effect Riverdance has had in improving standards in the traditional competitions. More participants means more rigorous standards and higher quality. "These days, dancers competing at open level have to be very fit," Brooks says. "They have to put more in - give up their football, for example - if they want to take it seriously."
While acknowledging Riverdance's role in making Irish dancing more palatable, Clerkin emphasises that its success owed a lot to numerous other professionals who had been strengthening and developing the tradition for some time. "I have to say that others of us saw the potential years ago but unfortunately didn't have the necessary money or the glitz," Clerkin says. "We've got such a firm basis with the discipline and what can be done with it that it cries out for elements of it to be played about with in a theatrical way. Irish dancing has always had people prepared to do something different with it - to move the upper half of the body, for example, and to experiment with other types of dance. Some might say that stops us being different but I think we can be confident enough of its beauty and skill not to worry that it will get diluted."
As the South Bank's workshop proved, it's not just those of Irish extraction who have been persuaded to take it up. June Armstrong, who lives in London but is from Barbados, was an instant convert in 1994. "I was mesmerised by Riverdance. The music really gets to you and I love the rhythms. The hardest thing for me is the discipline, keeping my hands by my side. We, as West Indians, like to move them and stamp our feet." Her whole family, which also includes a large Asian element, is similarly enthusiastic. "At Christmas, we all put Riverdance on, stand in front of the television and practise our moves."
Clerkin believes that the fact that Irish dancing is so rigidly different to other dance forms is integral to its popularity. "You've got dancers who are able to leap through the air and do amazingly dextrous things with their feet with not so much as a flicker of a muscle in the upper half of the body - the result is a unique dance form which everyone wants to come and look at."
The synchronised tapping of the feet on a vast scale has also captured audiences' imaginations. "Irish dancing adapts itself very well to tricky Balkan rhythms," Clerkin explains. "5/8 and 7/8, for example. It gets your head in a spin, as we're used to 4/4 and 6/8, but this, combined with the intricate footwork, is what makes the experience so exciting."
Perhaps the most significant change wrought by Flatley, Butler and company was a much-needed injection of sex appeal. Clerkin agrees: "When you look at the traditional costumes, masses of green velvet and embroidery, they're absolutely appalling to move in - it's like dancing under a pair of curtains," she says. "Suddenly, we've got shoulderless, backless, low-cut mini-dresses and long black legs. Of course it's sexy." She also points to the Mr Darcy effect; in her eyes, mean and moody also draws audiences in. "There is something very seductive about dancers with totally expressionless faces, while all this power is going through their feet."
Irish dancing may be at an all-time high but Clerkin is convinced that it will continue to get stronger through embracing elements from other cultures. "Look at how Irish music has developed with other world music," she says. "That's not to say that there's no room for tradition - there's room for both. But, ironically, by experimenting with new things, it makes audiences all the more interested in going back and seeing where it started and what it's all about."
But forget the sell-out world tours of Riverdance, the spoofs on Comic Relief and Guinness's decision to use Irish dancing in its pounds 4m advertising campaign for Harp. What more evidence do you need than the fact that, for the first time in Blitz's 12-year history, Peggy Spencer's ballroom dancing day has been toppled from its position as the No 1 crowd-puller. Thanks to Down by the Riverdance, even Peggy's been tangoed.
Blitz is at the Royal Festival Hall, South Bank Centre, London SE1 (0171- 960 4242) today and tomorrow