There are two anecdotes told about the founding of 11-piece folk group Bellowhead in 2004 – and both are true.

The most often told – it must be, it’s on Wikipedia ­– is that John Spiers and Jon Boden dreamed up the idea for the band while stuck in a traffic jam on the M25. The longer they were stuck, the more names they came up with of people they would like to join them in the band.

“It would only have been a quartet if the traffic had moved a bit quicker,” laughs trumpet player Andy Mellon, when confirming the truth of the incident.

“It’s part of the story,” he adds. “The other part of the story is that Jon Boden’s mum worked with Pete Flood’s mum in a charity shop.

“They were doing the ‘my son’s doing this’, ‘my son’s doing that’ thing that mums do, when they realised their sons were doing something similar and said, ’Our sons should get together’.”

Both stories perhaps hint at why the band are still together – with an almost unchanged line-up – nearly 10 years down the line.

“It’s like a big family,” says Andy.

“As with any group of people, you’ll fall out with somebody at some stage, but there are 11 people, so if you fall out with anyone, albeit briefly, there are always others you can talk to.”

He says the band work as a democracy.

“No one’s in charge,” he explains. “I’m 11th of a legal partnership.

“We also respect each other equally. You’re never harbouring a grudge because one person’s idea was chosen over yours. There’s no point as everyone has voted on it.

“There are differences in any group of people, but testament to our respect for each other and love for each other is that we are celebrating our tenth anniversary next year with pretty much our original line-up (nine of the 10 founder members are still in the band).”

The celebrations will include a birthday party in April at the Royal Albert Hall, no less.

There are downsides, of course.

One is that there are 11 diaries to co-ordinate; another that there are many more mouths to feed.

“To be brutally honest, an 11-piece doesn’t make that much money,” says Andy.

“You have to do other things to pay the mortgage and buy shoes for the children, which exacerbates the diary problems that might occur in a smaller band.”

These days, they travel around in two double-decker buses when on tour – one for the band and one for the instruments and crew.

The band’s bus, equipped with DVD player, a kitchen and, most importantly, a sandwich-maker, rolls into Birmingham on November 12, where they have a date at Symphony Hall.

“It’s our first time there,” Andy confirms, and he’s looking forward to it.

“I’ve heard it has amazing acoustics,” enthuses Andy, who reveals that he originally wanted to be a classical trumpet player.

“It’s the one all the classical musicians want to play at.”

Bellowhead have been to the city many times over the years, however. They’ve played at the Town Hall, rehearsed at one of the theatres and recorded the soundtrack for Archers spin-off Ambridge Extra at the Mailbox. Several members of the band – Jon Boden, fiddler Paul Sartin and manager Mark Whyles among them – are “huge” Archers fans, Andy reveals.

“They wanted a new version of the theme tune, which is quite folky anyway,” he explains. “I believe the producer at the time was a Bellowhead fan.

“Because it was for a young audience and we were quite young at the time, we got the call to do it.”

But it’s not just with producers and fans of Ambridge Extra that Bellowhead are a big hit. Their live shows are regularly sold out, while among their 20 nominations and eight gongs at the BBC2 Folk Awards are five for Best Live Act.

“It always comes as a huge surprise when we win that one,” says Andy. “It’s what we enjoy most of all.

“I think it’s that, before Bellowhead, we had all plied our trade independently. We are all old gig-dogs,” he laughs.

“I don’t think the folk scene had seen anything like it before.

“I think there’s also something about dancing like loons on stage.

“A band that navel-gazes isn’t going to get the audience up and dancing.”

* Bellowhead play Symphony Hall on November 12. Tel: 0121 345 0600 or visit www.thsh.co.uk.