Steeleye: spanning the decades

In fact, not a single member of Steeleye Span has been in the band continuously since the beginning. But here’s the distinction, and probably the key to its longevity: Once you’re in Steeleye Span, chances are good you’ll eventually return.

“We have had lots of people - well, not lots, actually. Not that many, really, because what they tend to do is go out and come back in again,’’ Maddy Prior, lead singer and a founding member, says this week from a London hotel where she and longtime fiddler Peter Knight are both staying. “We consider it a timeout, really.’’

Everyone in Steeleye seems to have had a hiatus and side projects, and funnily enough, the current incarnation is the longest-running in the band’s history. Reunited with Prior since 2002, whom many consider Steeleye’s heart and soul, the group is on the road again celebrating its 40th anniversary, including a stop tomorrow night at the Somerville Theatre.

A new album is also in the works, following 2006’s lively and contemporary “Bloody Men,’’ which proved Steeleye wasn’t interested in reliving the good old days. Besides, by now there’s a potent legacy at stake.

“Because we’ve been in it for 40 years, we all feel some sort of responsibility toward keeping it going. And that’s not because of financial interests,’’ Knight says. “If the music wasn’t happening, if we didn’t feel that we wanted to play music together, there would be no Steeleye Span because we’re certainly not a nostalgia band.’’

Knight admits Steeleye could easily have gone the way of other ’70s folk-rockers, especially since its commercial clout peaked toward the end of that decade after hits such as “All Around My Hat’’ and “Gaudete.’’

“When life throws things at you, you deal with it. When you’re in a band, if someone decides they want to leave, then you have the choice: Do you want to carry on or do you crumble?’’ he says. “And Steeleye has been through some quite interesting changes, but there was never a thought that that was the end of Steeleye.’’

Instead, the band has benefited from a revolving cast of players who have propelled the band into various directions, from purist traditional fare on Steeleye’s debut (1970’s “Hark! The Village Wait’’) to gradually tinkering and later fully altering the music’s landscape with rock arrangements and world-music flourishes.

Along with Fairport Convention (whose cofounding member Ashley Hutchings eventually left to help form Steeleye) and Pentangle, Steeleye was considered a group of mavericks building on England’s storied folk revival. They picked up the torch passed to them by singers such as Shirley Collins and Ewan MacColl. Four decades later, Knight understands how Steeleye was different from its peers.

“We were very arrogant,’’ he says, “and determined to make the music we wanted to make,’’ with little regard to bemused managers who thought the band should sometimes play it a bit safer.

“Music is there to be changed,’’ Knight adds, “and the argument isn’t whether it should be changed or not - it’s how you change it and why you change it. And Steeleye has been a band that’s been very sensitive to all aspects of that. So it’s a constantly evolving process.’’

But an ever-changing lineup could also have threatened the group’s tight dynamic. The fascinating footnote about Steeleye’s catalog is that, even now, those ’70s albums sound like they were made by the same musicians, albeit in the pursuit of new ideas. Prior says that’s a testament to Steeleye’s material as much as anything else.

“I think we’re unified by an attachment to British traditional music and working out from that,’’ she says. “We have written a lot of material, but it has always emanated from that kind of basis. That’s one of the things that makes it a different sort of band and why people can come in and out. The music and the songs are kind of what holds us together, and they’re not songwriter-specific that much. There is an element of that, but it’s not the whole story.’’

Still, that didn’t make it easier for the band members who had temporarily left to pursue other projects. Knight says it was distressing to hear what the group was doing without him.

“I couldn’t listen to those albums,’’ he says of the ones he didn’t play on. “My emotions wouldn’t allow me to. I suppose it took certainly a year before I could listen to what the band was doing. When I eventually did listen to the albums, I absolutely loved them.’’

Despite the numerous detours, Prior says Steeleye has never exhausted its love affair with traditional music. She says it’s sometimes a curse that the band can cull from such a vast repertoire, but that’s also a blessing.

“The great thing is how resilient the material is. You can rediscover it,’’ Prior says. “We lay songs fallow for a long time, and then we can green them up again and rethink them, and that’s lovely.’’

And, as you might expect at this point, the last thing on Steeleye’s mind is retirement.

“As long as we enjoy being with each other and making music together, then we’ll carry on,’’ Knight says, before cracking a joke: “in wheelchair-friendly halls. And that’s just for the band.’’

James Reed can be reached at jreed@globe.com.