It's fair to say that when Mumford & Sons first hit the limelight back in 2010, their rise was unexpected. They were a rousing folk band in the vein of acts like Old Crow Medicine Show, and they'd self-financed a debut album which was intriguing, courtesy of stirring ballads such as 'The Cave' and 'Little Lion Man'.

But headliner status in the States? Performing on national TV with Bob Dylan? Topping charts over in Australia and New Zealand? This was beyond their wildest dreams.

Everything since the release of their debut album, Sigh No More, has felt like Mumford & Sons trying to catch up with their runaway success. 2012's Babel leaned too heavily on the characteristics that made their first album so successful, while Wilder Mind leaned more towards electronic cues that tried to accommodate their place as arena headliners, but which didn't feel immediately natural for them.

That's not to say that either of these albums were bad - they were good - but as more and more folk bands tried to emulate Mumford & Sons' waistcoat-wearing, heart-on-sleeve lyricism (some call it 'nu-folk'), there's been a pressing need to reinvigorate their image.

Delta, the band's newest album, gets released this month. It marks a step towards a new direction that may actually work for them. Co-vocalist and guitarist Ben Lovett notes, "It feels like this might be the most important thing we've ever done with our lives."

Ben's out in LA getting ready for the album release. Along with the other three members of Mumford & Sons, he's on a press wheel up right up until November 16. But unlike when he's done this before, he doesn't mind doing interview after interview. As a matter of fact, he's actually pretty excited about talking about the new album.

"This one feels pretty different," he laughs, when I ask him whether he enjoys getting up early to talk about the record (it's 8am on in LA). "It's different compared to other times when we've been talking about new albums. You know, we've loved everything we've done, but there's something about Delta which feels special."

The album came about in the midst of an exceptionally busy couple of years, which saw them touring throughout 2015/2016 and producing a mini-album, called Johannesburg.

"We don't really believe in breaks," Ben tells me. "We were touring Wilder Mind in 2015/2016. In the middle of doing that we recorded Johannesburg. Then we kept on touring through 2017 and we did 70 shows that year. But towards the end of that year, we got an opportunity to try out some songs with Paul Epworth."

Epworth, an acclaimed producer who has worked with commercially successful artists like Adele and Rihanna, as well as cult acts like The Horrors, helped them unlock ideas they'd had rattling around for a while.

"We went in and did one song with him - sort of as a 'test day', because obviously you date someone before you marry. The first song we did was 'Slip Away' and that immediately felt like we were on the same page. It was interesting for him because he'd just come off from doing the latest Horrors record, and I think sonically he was in the space where we wanted to be. We were just off of doing Johannesburg, and lyrically and melodically, we were inspired by what he was doing. The dream is, you partner with a producer who not only has the repertoire and the reputation, but who also wants to do something important. We all just landed at the right place at the same time. That was about a year ago. And then we've been in and out of the studio up until about a month ago."

Who takes a commanding role in the studio?

"Paul's pretty dynamic. He understands when to take a backseat and when to step in. But, as a band, we need leading sometimes. For us to be able to maintain an authentic democracy, we can't self-elect someone between us to take charge. We have to appoint a project leader. So with Paul, sometimes he would sit back and say, 'That's a good idea, that's a bad idea.' Then other times he'd take a strong hand, saying, 'Right lads, we need to put a shift in tonight, and you all need to stay.' If it was Marcus or Winston turning to me and saying, 'Right, Ben, you all need to stay tonight,' I'd be like, 'Are you kidding? You do it!' It wouldn't come off in the same way.

"He's great though, he just feels like one of the boys. This summer obviously we had the World Cup. So we had that on the screen in the corner of the room, and for a month we were there watching every game, while Paul was making this music that was emotionally important. There's something about that that just works with Paul. It's why he's so great. He can be casual but he's also emotionally in touch."

Was the screen on for the England Croatia match?

"Yeah..." Lovett gives a wry laugh. "We went off on one and didn't come back to the studio. We took the night off after that result."

Mumford & Sons first performed in Ireland in 2009, when they made a small, but significant, appearance in the Academy's second room. From there, they built their fanbase in the country. By the time they headlined the Heineken Stage at Oxegen the following summer, the tent was packed to the rafters. Ever since, their live performances both here and abroad have become increasingly grander affairs. Now, it's just over 10 years since they first started. Are the band still as ambitious as they once were over a decade ago?

"Yeah, it's weird," muses Ben. "This week, that's felt like an important question. To tell the truth, I feel entirely unsatisfied by how far we've gone in our career so far. I feel like we've got so many more stories to tell, so much more that we can do on stage. So we needed a record that could set things up for us. But yeah, we just really want to do this. It wasn't a case of calling it in - it's about as far from that as possible.

"As far as ambition goes, I think it's something we gear up in each other. We set each other off and egg each other on. We have this healthy degree of competitiveness. So yeah, I honestly feel like, in some ways, this is us going back to day one. We've had an amazing journey and I'm very grateful, but I look back on it all and say, 'WhatÕs next?'"

Getting to the album itself, Delta eschews the anthemic veneer of Wilder Mind for songs that pack a more emotional punch. There's some clear radio-driven numbers in here, but the best songs come from a more introspective place. Considering that Mumford & Sons are now bona fide arena rockers, will it be difficult to get this album fully across in massive venues?

"Maybe," Lovett considers. "We're just figuring that out now. We already have some intimate songs in our repertoire, and amazingly people do shut up during those songs! We have those quiet songs like 'Cold Arms' that have been in our live set forever and that's always worked, so we're hoping the same will apply for some of these tunes.

"We want our sets to be as dynamic and full of contrasts as possible, to really accentuate the point of what we do. You take a song like 'Wild Heart', that's about as intimate as you can get. That was just a mic in the middle of a room, and we only did one take of that song. It feels so intimate and wears all its imperfections. It's almost like a campfire song. But that's as important to us as everything else."

When were most of these songs written? Was there an intense period of creativity?

"We've always been writing," explains Lovett. "We have the great fortune of having four great writers in the band. So we draw from each other. We had songs from the Wilder Mind period that didn't quite make that album and required more development. We had songs from Johannesburg. Honestly, we've got a lot more. We've got another 30 songs kicking around.

"One of the reasons why we called the album Delta is because the delta is the most fertile part of the river, and we feel like this is a really key period of our lives when it comes to creativity."

Certain songs on the album, like lead single 'Guiding Light', took a long time to create. Is everyone in the band patient with each other when it comes to road blocks like that?

"I think we are - that's something we've practised. We learnt patience from the last album when we were working with The National's Aaron Dessner. Aaron was like a coach for us in terms of patience. His experience with The National - a band that we loved so much - taught us the importance of patience.

"We also learnt to really flesh out each other's ideas. That's the other thing. If you rush something, you don't embrace the full extent of creativity. You know, someone might point to a glockenspiel in the corner of a studio and say, 'Oh what about using that in this song?' and your natural instinct is to roll your eyes. But we've learnt to see out those ideas. That's what we did with this album. We were like, "Okay, let's take a couple of hours. Let's explore these things'. We'd try stuff and a few hours later reflect on what we'd done.

"That wouldn't have happened five years ago. We were much younger, we were 18-20 when we started. We were impatient. We didn't listen to each other. We got into a cycle of deciding that certain things just didn't work."

Delta ultimately embraces some experimental colours as it progresses. The hip-hop influence of 'Rose Of Shannon' works quite well, while the title tune uses electronic music in a way that feels more natural than it did on their previous album. But it's the song 'Darkness Visible', which features American singer Gill Landry reciting Milton's Paradise Lost, which is most intriguing.

"That's a cool story actually," Ben says. "See as a band, we jam a lot. We love improvising together. And I think it was about 1am on a Friday night and someone started playing chords and we picked up different instruments, and we got into this kind of mantric state for about three hours. That's where the instrumental side of 'Darkness Visible' came from. Then Gill came and listened to what we'd made, and he listened to 'Picture You' (the track before 'Darkness Visible', which is intrinsically linked to it).

"There's a lot in that song that references Milton's Paradise Lost. And Paradise Lost is one of the most poetic and articulate explorations of depression that we'd ever read. So we all bonded over it, and Gill completely got the sentiment of the instrumental side of things. So we said, 'Why don't you read Paradise Lost over the track?' We never would've done that a few years ago. It was too out there. We've never done something predominantly instrumental. But we're proud of it. It feels as much us as anything else we've done."

Delta is out now.