The tiny room that serves as the venue for my meeting with a third of Belle & Sebastian couldn't be any more fitting. An awkward assemblage of '60s and '70s furniture that was likely picked up from a nearby East London market, it feels like an older relative's sitting room. The sofa is faded, the wooden chairs creak and the coffee table is stained with mug rings. To the side is a shelving unit on which stands the amp for a hi-fi system.

Stevie Jackson and Sarah Martin enter just as I'm getting set up. The two of them had flown down from Belle & Sebastian's home in Glasgow that morning. Jackson, spotting my immaculately maintained Moleskine offers to compare, pulling from his bag a black notebook held together with blue electrical tape.

"It's been around the world for the last three years," he says by way of apology, offering a fleeting glimpse at what's happened since the band last released a studio record. Five years have passed since the release of Write About Love, so it feels like it is time for them to release some new material.

"We didn't take much convincing," Martin says when asked what brought them back into the studio.

In actuality, the band had started working on new songs almost as soon as the Write About Love tour ended but plans for a new album were put on hold whilst Stuart Murdoch took the time to finish his debut film, God Help The Girl. As Martin points out, it was something Stuart had to take time out to do. "He realised at some point that he just had to gather momentum and do it otherwise it was never going to happen," she tells me.

The idea for God Help The Girl has been around since 2004 and was initially put on a back burner as the band worked on The Life Pursuit - though the way Martin and Jackson tell it, it could have easily replaced that record as the focus. Murdoch returned to the project after that record was released, finding more vocalists and releasing and album in 2009. The movie itself was finally shot in 2012 and saw its premiere at Sundance in January 2014. During this time, the rest of Belle & Sebastian assisted Murdoch in bringing his project to life.

"We all play on it," Jackson says, "but there was other stuff. Sarah was designing things for the film set, and I was putting together musicians for the soundtrack." Martin laughs as she recalls her attempts to get a job in the art department.

Martin had visited the production office, "which was a hive of activity," she says, in order to deliver some items to Murdoch and offered to help in any way possible. Before she knew what was happening, she was running about, delivering "odd bits and bobs" and helping out whoever could stake a claim to her time. "I was just kind of at a loose end," Martin says describing the experience. In amongst all of this, Murdoch also took the opportunity to cast Martin as a nurse in the film.

With God Help The Girl finally released, it was now time to, as Jackson puts it, "get together and get going with our career." When it finally came time to start work on their ninth album, having a small collection of tracks already worked up in some form helped to motive the band into getting the new record written and recorded.

"Those songs are going round your head," Martin explains, "and you don't want those songs to not appear on a record. You've got to get that record out."

The resulting record, Girls In Peacetime Want To Dance, is perhaps the Glaswegian act's most sonically diverse release to date. Taking in '80s electronica, euro-pop, baroque pop, calypso and even elements of shoegaze, it seems almost a world away from previous Belle & Sebastian releases, particularly the '60s pop of Write About Love and the gentle acoustics of If You're Feeling Sinister.

"A lot of it was in the writing," Jackson explains. In the early days, songs were built around melody and lyric. Stuart (or another member of the band, as the writing process opened up over the years) would put a song to the group -- and from there, they would work to discover what Jackson called "its stylistic identity." For this album, though, rhythm became the key component, with many songs taking a four on the floor beat as their core and being built up from there.

"But you've got your disco band and you said you wanted to do that," Martin adds. Whether conscious or not, there is a suggestion that this more rhythmic approach was something that the band were working towards or at least the sounds that come out on the record were becoming a much larger influence.

Despite this, the album isn't without its slower moments. Martin goes on to explain how 'The Cat With The Cream' was always seen as a pivotal moment on the record. A gorgeous ballad filled with soft strings and quiet guitar, it sits between two of the record's most upbeat tracks and is described as being the complete opposite of disco. Similarly, 'Ever Had a Little Faith?' is noted for not being a million miles away from the sound of the group's first three records.

"I think even the slow ones have a pulse to them," says Jackson. "Even 'Cat With The Cream' - that's got the same rhythm as 'Flash' by Queen but done on acoustic instruments and electric guitar." Indeed, as Jackson points out, most of the songs, even the quieter ones, have some form of driving momentum to them. Tracks like 'The Cat With The Cream', 'Today (This Army's For Peace)' and 'Nobody's Empire' might not have a disco stomp -- but rather they seem to pulse along, keeping a rhythmic thread running throughout the record.

According to Martin, this was something that producer Ben Allen really helped the band achieve. "You know what you're hinting at," she says, "and he just gets it set up." Allen, who has worked with the likes of Animal Collective, MIA, Cut Copy, Deerhunter and CeeLo Green, brought a whole new way of working to the band that encouraged them to explore their songs more and leave things more open-ended.

"Every other time we've recorded and done pre-production," Martin explains, "we've sat in our little rehearsal room in Glasgow with whoever the producer was and played through all the songs, deciding which ones we were going to do, locking down verses and putting extra choruses in. That's where the initial producing started, in the rehearsal room, shaping the songs and occasionally getting a little nudging with the arrangements." The band would then travel to the studio to record the album safe in the knowledge that they had agreed upon exactly what would appear on the record and in what form, the process was then about separating out the components of each song and getting it right from a technical point of view.

"But this time Ben said 'don't come with pre-production, we'll just do it before each song' and that was exactly how it worked," Martin continues. "We'd go in, and he'd have a little framework set up and would have an idea of who would play what instrument. If that didn't work, we'd switch it around. It was really, really liberating actually - a totally different way of working for us."

Jackson describes what he called a "telling" moment - Allen's continual references to the project being "our album," something they hadn't heard from another producer before. "It was kind of a giveaway in terms of him seeing it as a collaboration between the artist and the producer." Previous producers such as Trevor Horn and Tony Hoffer had been involved with the pre-production work but nothing to the extent of Ben Allen's collaborative approach.

One of the strangest things Martin had to deal with was Allen's seemingly lackadaisical approach to recording vocals. "He would just say 'oh you get on with some singing' and you'd ask 'do you not need to be here?' No other producer has ever not wanted to be there while you're singing. It got to the point where I actually got to fear when he did come in to the room." Allen, Martin explains, put his trust in his team, who he's worked with for years, whilst he'd throw ideas around and treat the group almost as they were a sample library. "He would chop things that somebody did in one part saying 'oh, that's really cool, but I don't know if that's working there, though' and ping it in somewhere else."

"It's just hip-hop sensibility," Jackson adds, "cutting bits and constructing it that way."

This jigsaw approach to music production was a key part of recording percussion. Richard Colburn would record a live take of the drum sections, before fixing anything he wasn't happy with. Once this was done Colburn and Allen would work to record every rhythm for a particular song in isolation so that Allen could construct the percussive portion of the track. Martin admits that, to an extent, this was how Allen used the whole band, adding that where they played something wasn't necessarily where that piece would end up. "It's a bit like cubism."

It was apparently a disconcerting experience for band leader Murdoch to cede so much control to a producer, but he quickly came around to it. In the meantime, he kept the rest of the band in the dark as to the album's overall concept by refusing to disclose even the album's title.

"I'd seen the title written down somewhere," Martin recalls, "but Stuart, he said 'I've got a plan, I don't want to jinx it.'" The title remained a secret until the day of the photoshoot for the album's artwork. According to Jackson, it immediately felt right -- almost as though it was an inevitable fact.

Head back on Thursday for part two of Robert Whitfield's interview with Belle & Sebastian.