Mumford & Sons' banjo player "Country" Winston Marshall has a terrible secret hidden under his bed back home in Fulham, west London. Next to his battered boots and scuffed trainers is a supermarket carrier bag that contains human remains, the clues to a previous life.
"It's where I keep my old hair," he says with an uncomfortable grin.
Today - in his boots and self-cut hair, raggedy beard and plaid shirt - Marshall looks like a hillbilly who might be on his way to chop logs or pull turnips. But back in the day he was a Rastafarian.
"I cut off my dreadlocks but I couldn't face throwing them away," he says. "They were so hard to grow, man. There's a lot of work goes into those things. Some people keep a diary or a photo album to remind them of their past lives - well, I've got hair. Who knows, one day maybe my grandchildren might want to see it."
I'm not so sure. When his grandchildren get around to checking out Marshall's life, they are probably going to be far more interested in what happened after the dreadlocks: the part he played in forming Mumford & Sons, one of the unlikeliest folk bands ever but one that this year has won over a worldwide audience.
Since they received their invitation to perform alongside Bob Dylan at this year's Grammy Awards, Mumford & Sons have been giving Coldplay a run for their money in America. Such was their Grammys hoedown that their album Sigh No More managed to sell more than 31,000 copies on the night alone. As well as Dylan, big hitters such as Taylor Swift have stepped up to congratulate and support them, and this summer's festival appearances have seen them return as conquering heroes. At Glastonbury they were mobbed, whereas a year ago they were newbies more likely to be mistaken as farmhands to the festival's founder, Michael Eavis.
Their rootsy look and feel hark back unashamedly to the mindset of pioneer-era America. And it doesn't end with the banjos and the plaid. This year, Mumford & Sons have played in far-flung venues in the Scottish highlands and rural Ireland. In the summer they undertook a US tour of railway depots travelling by vintage boxcar. Their lyrics speak of a yearning for more spiritual times. All of which is mightily effective but nonetheless strange because none of them has so much as seen a dust bowl or plucked a chicken. The singer and guitarist Marcus Mumford, 24; the keyboard player Ben Lovett, 23; the bassist Ted Dwane, 26; and the banjo man Marshall, 22, are nice boys from suburban London.
For young bands in west London - with the legacy of the Who and the Clash looming large - rock angst is usually mandatory. But Mumford & Sons bypassed all that. Growing up in leafy, affluent Wimbledon, south-west London, Mumford remembers that his first record was Dylan's Blood on the Tracks - his mother's copy and her only concession to "modern". But if anything Mumford was jazz-bound. He and Lovett attended the private King's College School in Wimbledon together and played Count Basie tunes in the school's big band. Mumford went one further - he looks suitably queasy when recounting the name of his free-form jazz side-project ... Detente.
But two important things changed that. His brother James gave him a copy of the Coen brothers' film O Brother Where Art Thou. The Coens' retelling of Homer's The Odyssey via the adventures of three convicts escaped from Mississippi State Penitentiary appealed on several levels. First, the classical and religious undertones (Mumford would later study a year of Classics at Edinburgh University). But most importantly, it was the film's soundtrack and then, when he was 17, a driving licence that really clinched things for him.
"It's a gold mine," he says of the soundtrack. "That was it. I just couldn't stop listening to it. And then I learnt to drive. I defy anyone to get in a car and drive with that soundtrack on. It creates a journey. And like John Steinbeck says, a journey is a person in itself. It has to have an element of the unknown and mystery. England doesn't have the wide-open frontiers that America has but with those bluegrass tunes on the car stereo you are almost there."
Although Mumford had gone to university, the Bosun's Locker - a now-defunct nightclub run by Marshall - in a cellar below a Cornish pasty shop on London's King's Road became the locus for the small but lauded "nu-folk" scene. He travelled down regularly to play drums for various folk-tinged hopefuls.
"You'd struggle to find a scene less like an actual scene anywhere," says Mumford. "Scenes are supposed to have a look and an ideal and a certain exclusivity. We didn't. We welcomed anyone and we played whatever came to hand. But, yeah, if 80 people in a hole in the ground under-age drinking is a folk scene, that's what it was."
The other band members don't have very folky CVs either. Lovett was in an indie band, Hot Rocket, with a single called Do Do Do airing on indie radio. Dwane was in a proto-punk band with the distinctly un-country name Sex Face. Meanwhile, Marshall had been a Backstreet Boys fan at school and had been playing the banjo for only a year or so.
Still, the Bosun's Locker spawned some notable talent: Laura Marling, Noah & The Whale as well as Jay Jay Pistolet among them. Mumford, Marshall and Dwane played as Marling's backing band. Occasionally they claimed the spotlight for themselves as Marcus Mumford & His Merry Men, a shambolic and overstaffed prototype for today's band.
In October 2007 the key foursome peeled away and wrote three songs at RMS studios in Putney, south-west London: White Blank Page, Awake My Soul and a now-discarded track called The Liar. Mumford & Sons was born.
"We called ourselves Mumford & Sons because we liked the idea of an old-fashioned, family-owned store," says Marshall. "If it really was a store it would sell cheese and whisky, cigarettes and tools. A general store selling stuff you really cannot live without. And we tried to write music that felt sort of natural and... necessary."
Adds Lovett: "We sang in harmony in that studio and it clicked. Four felt like a family. And then we just kept this ethic of jamming, writing, performing from scraps of paper stuck to the kick drum and then honing it afterwards. I'm going to sound like a complete w****r now but I don't care: the idea is we serve the song. And the songs were served by us being a four."
The Bosun's Locker scene has since fragmented. Noah & The Whale have evolved a new sound with their recent album, their third, Last Night On Earth. Pistolet is no longer a folky troubadour but is now Justin Young singing with the Vaccines about sex after a break-up. But Mumford & Sons have stuck with their country palette. And Marcus Mumford has not migrated from the Laura Marling drum stool to frontman by accident. Those first two songs, White Blank Page and Awake My Soul, set an important, quasi-religious tone.
Mumford was born in California, where his parents, John and Eleanor, were involved with the evangelical Vineyard Church (coincidentally, Dylan had a born-again experience at a Vineyard Bible study class in 1978). Now the Mumfords' website is unequivocal: "We believe... the whole world is under the domination of Satan and that all people are sinners by nature and choice".
Mumford did not absorb his parents' faith entirely. But its legacy is there and in the music. Sigh No More is full of references to a "design, an alignment" and the grace that will come "when you know the maker's land".
"Am I evangelical?" he asks, repeating my query. "I don't think you are wrong about faith but it's not evangelical. We had a conversation about religion at the beginning and said: 'This is not what this band is about.' We'll explore the idea of loving your neighbour but also of [cutting up] like we do on Little Lion Man. I am not a fan of organised man-made religion. But faith is important to me.
"Could I be a preacher? I can't imagine anyone listening to me without thinking: 'Why should I listen to that fat w****r?' I'm a musician and a romantic who loves the road... If we have a belief, it's that we can make music and not be part of the machine - showbiz or whatever you want to call it. We live in a mad time where everyone thinks 'celebrity' rules everything. It doesn't. Having a showbiz career is not important. You can connect with a room of 50 people and it can be the greatest feeling in the world. I don't want anything more than that. I don't see anyone like a preacher man or Bono when I look in the bathroom mirror. I see a man who needs to play some football to stave off getting another chin."
As for that "romantic", there have been rumours that he has begun dating the British actress Carey Mulligan. "You've done your job: you've asked," he says, lighting a cigarette. He blows a puff of smoke into the London sky and sighs.
Given their recent success, their natural reticence makes them uneasy about being a part of "the industry". At the Grammys in Los Angeles they glad-handed with Usher and Gwyneth Paltrow and it felt OK. But one day after rehearsals at the Staples Centre they became trapped in a lift with Justin Bieber and four of his burly security guards.
"We're not denigrating anyone," says Mumford. "My goddaughter loves the dude. But it is amazing to me that we are supposed to be in the same world. For us, the acid test for any artist would be: 'Could we give this dude a mandolin and just jam?'"
The Dylan duet if anything posed the opposite problem. After an introductory fist-pump at rehearsals, they launched straight into Maggie's Farm and the Mumfords' own The Cave. But less than a minute before they hit the stage for the official awards performance, Dylan wanted to change the arrangement.
"That was a definite moment," says Marshall. "I can't promise you we wouldn't have f***** the whole thing up just out of sheer nerves. Luckily even members of his band were like: 'Come on boss, let's just leave it like it is'. I get the feeling Dylan is pulling that s*** all the time."
Mumford has the final word:
"We are glad we didn't leave our hearts there. It was fun but it's not really us. LA is not us. Awards are not us. We are from England. We like the road and we like the pub. We don't want celebrity. We don't feel good at the awards dinner table. It's not where music happens, is it?"
Mumford & Sons might appear quaintly olde worlde, the sort of boys to restore an aunt's faith in today's youth if they popped round for tea. But this belies the fact that as a live band they totally rawk. I saw them play the Olympia in Dublin earlier this year. There is something in the yokel stomp of their music and the passionate yearning of their lyrics that drives fans wild. And for them, the live response is what it's all about.
"We don't want the audience to sit down and watch a performance. We want to invite them in, see the whites of their eyes," says Mumford. "We feel the job is done when there is a physical reaction."
Next year will make them one of the biggest and most unusual bands in the world, especially if the new music they are writing for the new album is anything to go by. They invite me to a low-ceilinged rehearsal space in Putney, and they plug in and play. Love Was Kind and Broken Crown are impressive enough. The latter's lyric - "Crawl on my belly till the sun goes down/I'll never wear your broken crown/I'll take the road/I can f*** it all away" - is bleaker than anything they've done before. But another new song with the dual working titles Hopeless Wanderer and Skies I'm Under begins with an ethereal wash of treated banjo, before exploding into an epic chorus that runs: "Hold me fast 'cause I'm a hopeless wanderer/I will learn to love the skies I'm under". It's a blistering stomp that sounds bigger tighter and more powerful than in Dublin. The words "'hold" and "fast" were tattooed on the captain's knuckles on the ship in the Russell Crowe film Master & Commander, one of his father's favourite films, says Mumford.
"And that's what we are doing," he says. "We are riding the wave and holding on to the stuff that really matters as hard as we can."
As they prepare to release their second album, Mumford & Sons, in addition to four extended plays, have recorded one album that has spawned the release of four singles. The details:
SIGH NO MORE (October 2009) The debut album entered the UK Albums Chart at No. 11 and peaked at No. 2. It was chosen Album of the Year at the 2011 Brit Awards and was shortlisted for the Mercury Prize. It has sold more than 1.6 million copies.
LITTLE LION MAN (September 2009) Released just ahead of Sigh No More, the band's first single spent two weeks in the UK Top 40 but enjoyed greater success in Australia and the US. It was nominated for Best Rock Song at the 53rd Grammy Awards.
WINTER WINDS (December 2009) Fraser McAlpine of the BBC Chart Blog called this song an "amazing Christmas carol equivalent", and Marcus Mumford has said it is his favourite to perform live. It peaked at No. 44 in the UK.
THE CAVE (March 2010) Another that was especially well-received in Australia and the US. It was featured in the pilot episode of the Fox Network's drama Lone Star.
ROLL AWAY YOUR STONE (June 2010) Topped out at No. 144 on the UK charts, and thus the band's least successful single thus far.
Two other singles charted because of digital downloads:
WHITE BLANK PAGE (November 2010) Hit No. 134 in the UK.
TIMSHEL (August 2011) Hit No. 71 in the UK.