After performing at the Grammys, the quartet found itself number two on the music charts. How did it get there?

Reuters/Luke MacGregor

Star-spangled success remains but a dream for most British bands that attempt to break out in America. For Mumford & Sons, it's fast becoming a reality.

Following the band's performance at the Grammys on February 13—where it was nominated in the categories of Best New Artist and Best Rock Song for "Little Lion Man"—its profile has soared. Mumford & Son's debut Sigh No More rocketed to Number Two on the Billboard 200—it's currently at Number Three—helping the London band become the first British act since Coldplay to sell more than a million records in the US. The band's post-Grammys success is particularly remarkable when you consider they didn't even win an award, and that the acts who did win—Best New Artist winner Esperanza Spalding and Best Album winner Arcade Fire, for example—have not enjoyed the same surge. Last month, the band sat on the charts between Justin Bieber and the pop music compilation album Now 37—how did a folk rock quartet from London get there?

Listen to music from London's folk scene

It's a long way from Bosun's Locker, the 40-capacity venue in west London where Marcus Mumford began road-testing his early efforts in 2006, after dropping out of Edinburgh University where he was studying Classics. That pub, which has subsequently closed down, became the epicenter of the "west London folk scene"—a musical community that spawned such acts as Noah and the Whale, Cherbourg, and Laura Marling, Marcus Mumford's former squeeze.

Cherbourg bassist Kevin Jones, who now runs Communion, a hugely influential London concert series, with Mumford & Sons' Ben Lovett, remembers it well. "It was a tiny little place under a passageway," he says. "There were lots of really talented people kicking about—Laura Marling, Marcus Mumford, Charlie Fink [Noah and the Whale frontman]—just swapping songwriting ideas and making friends. It shut down prematurely and, at the same time, we were given an opportunity to start Communion at Notting Hill Arts Club. In that sense, I guess, it is a logical next step from Bosun's Locker. But it wasn't a conscious decision; it just kind of evolved. We now have nights in nine cities, including one in New York, which is going really well."

Listen to music by Mumford & Sons

Meanwhile, after a brief spell as Laura Marling's backing band, Mumford & Sons were formed in December 2007. Over the next few years, it steadily gained a reputation as a fabulous live act. In 2010, the band was one of the main attractions at Glastonbury Festival; later that summer, at Hop Farm, it drew a bigger crowd than Bob Dylan (although I'm guessing the boys refrained from mentioning this to Bob when they performed together at the Grammys). The growing crowds have been greeted by a live show that reaches an almost spiritual intensity. Mumford transforms into gutsy, gravelly frontman while his Sons—who aren't really his sons at all, but contemporaries Ben Lovett, Ted Dwane and "Country" Winston Marshall—provide hearty harmonies and barnstorming backing: it's an irresistible combination.