There was no stopping the performers at the 33rd Lorient Interceltic Festival, despite sweltering temperatures, writes Mary Phelan.

You can't really argue with 600,000 ticket buyers. Or with 4,500 performers. Or with 800 or so volunteers, each of whom gives up a week's precious summer holidays to help with everything from selling those tickets to ferrying artists around on Harley-Davidson motorbikes. Festival Interceltique de Lorient, or Lorient Interceltic Festival, in Brittany, is now in its 33rd year - and it is bigger, bolder and more successful than ever.

On Monday morning the Irish delegation of some 170 singers, dancers, musicians and pipe-band members straggled off the Lorient Express, the charter flight that has become part of the mythology of Irish traditional music, tired but happy to be home and, for once, looking forward to westerly winds and scattered showers.

For 10 days they had sweated it out with their Celtic cousins, singing, dancing and, in full regalia despite sweltering temperatures, taking part in the street parades that are a defining feature of the festival. They also, of course, continued the tradition of being the life and soul of the party, playing music until after dawn.

This year the group included Seán Garvey and Brid Ní Mhaoichiarain, singers from Connemara, Siobhán Armstrong, a harper, Planxty Ó Ruairc, a dance troupe from Limerick, and two pipe bands, St Colman's from Cobh, in Co Cork, and Thomas Davis Memorial Pipe band from Newry, in Co Down.

Pete McCarthy, the writer and broadcaster, put in an appearance at the festival's book fair, launching the French translation of his best-seller McCarthy's Bar: A Journey Of Discovery In Ireland. At the art salon the work of Paddy Lennon from Dublin was on display.

Headline events this year included a piano recital by Didier Squiban, a Breton virtuoso pianist who shared the stage with the Irish musician and academic Micheál Ó Súilleabháin, and a gala night of female performers, among them the fiddle supremo Eileen Ivers, the Scottish singer Karen Matheson and the Clare accordionist Sharon Shannon.

But the big acts make up only part of the action. With more than 25 official events each day, and hundreds of smaller ones, you're spoiled for choice. Music forms the core of the festival, but Celtic culture is celebrated, explored, extended and promoted in all its manifestations.

The festival started as a piping event, and pipes are still at its core, just as they are core to Breton culture. Most towns in Brittany boast a bagad, or pipe band. The sound of the pipes permeates the festivities. The formal piping world is driven by competitions, with several prestigious contests held during the 10 days of Lorient's festival. They attract contestants from as far away as New Zealand, Australia and Canada.

The sight and the sound of pipe bands parading in full regalia or of a kilted solo piper belting it out on a cafe terrace or a street corner is the norm in Lorient. This year's record temperatures dampened none of the enthusiasm, and yards of heavy tartan were still proudly paraded even as their wearers melted.

Performers from Asturias and Galicia - Celtic relations from northern Spain - always add an exoticism to the mix. This year Asturias was also focused on by the festival - each year it concentrates on a country or region - so a large marquee was devoted to the culinary and cultural delights of this small but committed bastion of Celtic culture.

Although it is still anchored in traditional forms of cultural expression, Lorient Interceltic Festival has developed significantly since it began. Lead by the eloquent, loquacious Jean-Pierre Pichard, it has taken a dynamic approach to the culture it reflects, commissioning works, pioneering initiatives and even developing new art forms.

The Nuits Magiques, or Magic Nights, are a case in point. Based on the military tattoo but incorporating dance, singing, visual projection, theatrical lighting and pyrotechnics, these dramatic and evocative shows, which fill the local football stadium, have become a hallmark of the Lorient experience.

Celebrating a shared Celtic heritage, and including Breton bagads, Scottish and Irish pipe bands and banda de gaitas, the Galician and Asturian equivalent, they culminate in a spectacular 20-minute firework display choreographed to the Riverdance finale. Heady stuff.

The festival's commissioning of work means it has contributed to the development of both indigenous musical traditions and a more global Celtic musical identity. Shaun Davey's Suite Celtique De Lorient, commissioned in the early 1980s, subsequently became The Pilgrim Suite. Alan Stivell's Celtic Symphony also owes its origin to the festival.

This year it was the turn of Ó Súilleabháin, one of five composers commissioned to write a work describing their country. Under the umbrella title Jigsaw, these compositions for orchestra, traditional instruments and voice brought veterans such as Ó Súilleabháin and Scotland's Eddie McGuire together with younger composers such as Pwyll ap Sion of Wales and RamóPrada of Asturias, the hit of the evening, for an ambitious and moving premiere.

Ó Súilleabháin's encounter with Squiban, the Breton pianist, was another example of imaginative programming. Although they are comparable in background and stature and are both strongly influenced by jazz, they have strikingly different approaches to the traditional idiom. Ó Súilleabháin stays within the parameters of tune structure, melody and rhythm while Squiban uses traditional melody lines as a basis for improvisation.

Celting Pot was another ambitious musical creation. A new work by local composers Marc and Franck Steckar, it pitched bombardes - traditional Breton wind instruments - against a vast array of percussion, from steel drums through marimbas and vibraphones to congas and bongos, with a brass section thrown in for good measure. It also featured the percussive aplomb of six dancers from the Irish troupe, apparently now de rigueur for any grand finale in Lorient. Michael Flatley eat your heart out.

Ireland's contribution to the success of the festival has always been central, and this year was no exception. Most of the Irish events, and there were many, sold out. Among them, given its huge success last year, was a second Women of Ireland concert. Indeed, women were strikingly prominent in Lorient. Topping the bill on Sunday, for the festival's final concert, were Sharon Shannon, Eileen Ivers and Karen Matheson.

Festival veterans such as the fiddle teacher Kathleen Nesbitt and newcomers such as Gane - eight young and extremely promising women - showed that sisters are doing it for themselves, doing it very well and having lots of fun in the process.

The sight of 19 women jamming at the end of the Women of Ireland concert was wonderful. So too was the assured pureness of the singing of Brid Ní Mhaolchiaran, a joy amid the innovation and fusion of influences.

As Nicholas Carolan, director of the Irish Traditional Music Archive, pointed out, the festival demonstrates what is possible. "In Ireland we think of the Willie Clancy [Summer School\] week as a huge thing. But this just shows the impact that having such an enormous population base can have on traditional music. It brings the whole thing to a different level in terms of performance, interaction and experience."