"You've got to have a start and and end to a story," Diamandis tells me matter-of-factly as she sips from a cup of camomile tea. We're talking against the background clatter of crockery and stainless steel in a rustic-chic nook cafe in London's Primrose Hill. "You have to do it publicly. Could you imagine if I'd just let her fade away?"

Diamandis had prepared herself for the end of Electra Heart's long ago, with a lifespan that was always predetermined. "As soon as I'd finished the record and "Primadonna" came out and I went onto that treadmill of working promo, I already knew what I wanted to do with my third record. I already knew it was going to be completely different," she says. "I was really grateful for the experiences and opportunities that Electra Heart gave me, but I will never do it again. It was very early on that I understood that."

The South Wales-born singer switches her smile to full-beam as she speaks, alert and eager-eyed. There's relief mixed with excitement in her voice as she recounts the psychological detox of moving on from her last record: "I can't imagine in a million years putting that wig again... it was a one-time thing. I do miss it sometimes; it was such fun..." There's a beat, the briefest of pensive flickers, before a caveat: "...but you know what? I don't think I could ever do it again."

Before the soil had even settled on Electra Heart's grave, Diamandis had vanished. The album's final tour ended last June and she whisked herself back to London for six months of semi-solitude. "I didn't really want to speak to anybody. I was pretty low-key," she admits. "I don't know if I'm 'phoenix rising', but I do feel like a very different person.

“I think I used to believe that being depressed was part of my personality or that I was born like that, but it's quite shocking to realise that perhaps that isn't the case.”

"I felt like I hadn't changed between 18 and 27, which is a really long fucking time to not grow up or not deal with certain issues. I feel lighter now. I feel very different. The weirdest thing was that it was almost overnight. I'm 29 and I've not experienced this in my life before. I think it was something that I was looking for. The previous years when I was projecting cynicism, or when I was being snarky or whatever, I was myself all the time."

This veiling was quite literal at times - Electra Heart was a completely new identity. "I knew that wasn't true to who I was as a person, or how I felt like who I wanted to be, but when you're not happy with yourself like that, it's very hard to show it, and it's very hard to change your behaviours."

"It was almost like I had been burdened by something my whole life and then suddenly that went away..." she explains. "I can't even describe how amazing it is... you suddenly realise why people are happy and why people enjoy things. I think I used to believe that being depressed was part of my personality or that I was born like that, but it's quite shocking to realise that perhaps that isn't the case."

Still, mystery surrounds the catalyst for this fresh perspective on life: "Maybe I was ready to change. Maybe I was ready to leave a lot of things I'd held onto in the past behind. I don't know if that happens to other people when they hit a certain age, or maybe some people don't even have those issues to begin with. Perhaps it's not very common, but I know that it was important for my future."

"Shit still goes down in life whether you're happy with yourself or not," she says, glancing at the diners reading newspapers emblazoned with headlines about ebola and political dichotomy. "Happy is the wrong word. It's more to do with being at ease with yourself as a human being; liking who you are. Being truthful with who you are as a person and understanding that. If there were no troubles, I don't know how I would write."

"I think this new album is much more reflective," she affirms. "It's also centred around extremely different things; half of the album is about a relationship that I had to end. It's not something I feel good about, and it's not something I'd really addressed before in my songwriting. In pop music in general it's always this spurned ex-lover type of thing, but this time it wasn't that at all. It was more like the guilt that you have to deal with that comes from hurting someone else. It's just as hard as being rejected or dumped."

Going on to explain the challenges of new album FROOT, Diamandis becomes a little more animated. "I'm okay writing alone, I have a lot of discipline for that, but with production..." she laughs, "it's never been my favourite thing in the world."

Electra Heart came with a long list of production credits - "It was like the bible of pop producers at the time," she says, exasperated. "But that's what you get when you co-write with a lot of people and each person is producing their own song." Despite her aversion to production, the invigorated Diamandis took half of the reins when making FROOT, preferring the company of one producer as opposed to a rotating cast. "I was working with David Kosten [Everything Everything, Bat For Lashes], who is amazing, and... just him. That's all."

The landscape that bore FROOT was considerably more isolated than Electra Heart's foundation. As well as confining herself to her own thoughts after putting that record to rest, she actively sought to create alone. "In the past because I was new and I was someone who really needed praise, I very much listened to other people, perhaps when I shouldn't have. So because of that, on FROOT, I wanted to create the whole thing. I think one of the biggest challenges was saying what I wanted to do for once. Whoever you are as an artist, you have to know who you are so that you can do what you want to do... so that no one's going to tell you what your identity is.

"I think my confidence as a songwriter has improved just by listening to my instincts and believing in my own abilities."

Listening to the finished portions of FROOT it's evident that the Marina and The Diamonds sound has shifted once again. While debut The Family Jewels, skirted indie-pop and the realms of synth-based noise, its follow-up was a palpable dancefloor-pop explosion that scored her a number one in the UK. FROOT explores darker themes in a darker way, sometimes veering closer to The Family Jewels by using organic instruments to greater effect and swapping out the instant gratification of hook bombast for a more lyrical focus.

“It's not about being pop or not pop, or electronic or not electronic, it's more about feeling the groove in the music and knowing there are real musicians playing it.”

"I feel like the songs I identify with most - not the ones I think are the best, but the ones that speak to me - are "I Am Not A Robot", "Mowgli's Road" and "Hollywood", which are kind of like these fusions of alternative and rock music," she explains. "I don't think there was a concerted effort to go back to that... that is just my sound. That's what I'm interested in. It's not about being pop or not pop, or electronic or not electronic, it's more about feeling the groove in the music and knowing there are real musicians playing it. I think it's something that I've been trying translate for a long time."

One of the biggest bugbears to address when sculpting FROOT was the distance between Diamandis' recorded and live sound. "It always really frustrated me that I wasn't able to achieve the consistency, so when I started writing this album and I was looking for a producer, I remember saying to my A&R that I need to be produced as a band, because that's how I feel on stage. I feel like I'm the frontwoman of a band and in two albums, that's not been communicated.

"Now I finally feel like I have done that."

Recorded live in London, Diamandis' writing process fleshed out as the record hit its final stages. "I did start out doing it all electronically - kind of how I did the first album - but all the drums just sounded shit. I was like 'well, I know musicians...' and David Kosten knows people - obviously Everything Everything - I went to a show, met them and did a bunch of stuff.

"I got Alex and Jeremy from the band to do guitars [on FROOT] - I'm a massive fan of them - Jason Cooper who drums in The Cure, he did all the percussion on the record. It's definitely got their influence in there."

Diamandis suddenly turns the tables on me, leaning in: "You know, you're the first person to hear the new songs, outside of labels and management," she says questioningly.

While FROOT isn't entirely finished yet, I was given the chance to hear a hefty portion of the new record ahead of its April 2015 release. The sassy "Better Than That" sticks out as a future heavy-hitter, doused in wah-wah axes and classic funk and rock delvings. "It is, it's like classic rock!" Diamandis enthuses. "That's why I wanted you to hear that one actually. I added it at the last minute... it's still unmixed... but for me it's really important for the sound of the record 'cause that was one of the first songs I wrote and that heralded the new shift in direction."

A sparkling ballroom ballad that deals in existential motifs, "Immortals" is another impressive cut and arguably the darkest thing she's ever written. "It's a really universal issue discussing how you leave your mark and how it's really important to preserve memories and remember people," she says, offering an explanation of its genesis. "I started writing that song when I went to a war memorial in Poland. Something that somebody I was with just struck me... they said 'It's not a very beautiful memorial, but it deserves to be visited to keep their memory alive.' That's how the song - well, the lyrics - started."

Listening to the track recalls The Family Jewels' "Are You Satisfied?" and its Kierkegaardian take on the meaning of life. "They're not consciously related, but it's a good point. I guess both are talking about that need to feel fulfilled or live that kind of life that you would want to. It's hard. It's hard to be happy all the time - it's not natural - but that's what people want to be."

On her first two albums, Diamandis wasn't necessarily subtle but FROOT finds a prevailing sincerity. "I think the cynicism's gone a bit. I guess it's probably because I'm happy. It sounds very uninteresting, but I think when you aren't happy with yourself you tend to be much more cynical about life."

Will the self-destructive streak from her first two albums return in light of this emotional rebirth, I ask? "I think it depends what's happening in your life. I'm just thinking about relationships as they're the biggest source of creativity. This time, because I'd had a very different experience in a relationship, I'd written about different things. I see albums as chapters of your life. That's it. It doesn't matter if it's commercial or not commercial, a product or not a product... for me it's a way of chronicling my life. For the fan, to see how someone progresses... I mean I love seeing that in artists I'm a fan of. It's because you become attached to them, and you hope that good things are happening for them and certain things are mended in them.

"To see that progression is really satisfying. That's what I'm here for, that's what I'm interested in doing."

Diamandis is keen to note that FROOT isn't entirely dark. "It's almost celebrating being happy. Maybe it's the same sort of thing I'm talking about in that I want to live an amazing life and I want to live the best life that I can. It's all to easy to complain and be cynical about things, but I feel like this emotional shift I've had means I don't feel like that anymore. I really want to enjoy life, whatever that life entails."

A distinct lack of character-driven narratives also characterise the new record over its predecessors. "There's no kind of conceptual thing that surrounds this record," Diamandis explains, "except perhaps a little visual packaging. There wasn't a need to. I feel like Electra Heart was very much more about identity and expressing various female archetypes through character, which I really enjoyed and was relevant to me at the time, but now? I don't relate to that anymore."

I ask if there have been any other changes between Electra Heart and FROOT? "I used to listen to my team a lot, and I think that came from a lack of experience and maybe not being very self-assured, whereas now... I tried a lot of different things.

"For example, Electra Heart was so incredible in that it really changed the way that I wrote, and I don't think I would've written this album if I hadn't been through that process. I would be observing people like Diplo and Dr. Luke, and I found after that was writing in a much more free way, whereas when I was writing on my own with a piano I was really just stuck to it and I became quite limited, like I'd reached a certain point.

"I think it was down to the fact that they were giving me instrumentals to write on, and I was like "well I can make an instrumental..." so I started making these really shoddy ones at home and then found that completely and suddenly opened up my whole songwriting sphere in a really amazing way."

I mention that the new record seems like a more obvious successor to The Family Jewels. "I totally know what you mean," she says. "It does feel like a very natural progression from where I left off on the first record. I see Electra Heart as the anomaly. For example, after FROOT, what if my fourth record is a continuation of the that? Then Electra Heart will always be the anomaly, it'll always be second, in that sense."

The anomaly of Electra Heart meant it didn't go down as well in the USA as the UK. "It was an American-produced album, all of the imagery was referencing American culture... it made complete sense that it would be received better there, but let's not forget I pretended to be a completely different person. If I hadn't done that and I'd still done a pop album it might have been easier to digest for the UK.

“I'm always going to want to experiment with production and with sound so everyone had better get used to the fact I'm probably going to change with each album!”

"I can't control what people think of me and what people are going to think of anything I do in the future. I think for the first time, I feel comfortable. I know I've struggled in certain parts of the past five years, as most artists do when they're starting out, and I know I'm always going to want to experiment with production and with sound so everyone had better get used to the fact I'm probably going to change with each album!"

Now, with this light shining once more upon her roots, there's scant fear that her more recent influx of fans will balk at the change arriving on FROOT. "I think I will always - god willing - have a fanbase in America that's really strong," Diamandis says. "I think a lot at the moment are pop fans, and I think that's how they discovered me, through 'Primadonna' and 'How To Be A Heartbreaker'... but I also feel like most of them are in it for the ride, and they're very interested in and supportive of what I do next in terms of developing as an artist.

"You never know how it's going to be received. I hate saying the word 'rock', but it is kind of like rock... but with pop," she laughs, before retracing her steps: "I guess it's an alternative pop record. Visually I've definitely been interested in the '70s, for sure. I really like jumpsuits, I'm really liking suits at the moment.

"I suppose still being feminine but maybe dressing in a way I didn't before. I used to be a lot louder, a lot more 'pop art', but now I'm 29 I feel different, and I want to dress differently."

The visual element of Marina and The Diamonds has never necessarily been crucial and the striking imagery that accompanied both The Family Jewels and Electra Heart cemented itself as a part of Diamandis' persona. FROOT does little to derail that trait: "In the beginning, when I did my first photoshoot, I was trying to describe it as like blending neon with nature. It's like a cyber La Dolce Vita, or a sci-fi Sophia Loren, or a futuristic Liz Taylor. It's about taking these iconic figures, these feminine icons, and interpreting them an a modern way. I wanted a '50s or '70s look but with something that's artificial."

Of course, that also translates to Diamandis' ambitious live plans for 2015. "I want to create a cyber garden on stage... like an electric orchard with these huge orange trees. I've already got some grapevines that glow. I want the merch stalls to be like a market, so the T-shirts are in little crates, and have fruit punch available... it's a world I can't wait to get into and build. We're even thinking of having life-sized fruits on stage... but like disco ball versions.

"So we'd have this massive bunch of cherries but it's a working, turning disco ball. I want it to work anywhere, from somewhere that's five hundred capacity to somewhere that's five thousand ."

In a way, the visuals that envelop Diamandis' albums are a prudent way to get into her complexities. "The visuals are always a helpful way of expressing to people what stage you're at... I mean I haven't really been around for about two years - certainly not in the UK - and I guess it can be an indicator for people. I think it will always be important to me, but it might not be as big a tool for expression when it comes to FROOT as it was for Electra Heart, because of the way that record had been produced, and because I hadn't had a part in that. The visuals were my way of expressing what I wanted to say so I went to town with it."

When it comes to the musical and technical side of production, Diamandis' world hs been exponentially expanded. "I've learned a lot more about things like drums, which I never really cared about before. They were always second place! The only things that used to matter to me were melody and lyrics, and still, when I listen to a song, I'll only ever zone in on those things. But I feel like I've become much more able to tune into that sort of thing now, which is interesting. I really enjoyed being part of the whole production process, and I think in the future I will produce my own album, with perhaps only an engineer to help,"

I ask her why the album's title track was the best way to welcome people into that turning point. "Lead tracks are funny. Whatever you lead with, it's going to put out a message to everybody watching and who's a fan as to how you're going to progress. If I'd come out with "Blue", probably my biggest sounding song, it would be like "oh, okay, this a huge pop campaign, let's do the whole Top 40 route" and I'm just not here for that anymore.

"If it happens, it's fantastic, and I still consider myself part of that world, but I don't want to have to adhere to or rely on that anymore. It's completely tiring; artistically it's fucking draining [but] with "FROOT" it's a wildcard. I think a lot of people assume it's about sex, but it's not. Strictly. Most of it is not. It's really about being ready for happiness, and being ready to love somebody, and being fully-realised as a person. I like that it's a really positive message to start on. I needed that. It would've been easy to go with something like "Happy", which is a ballad and kind of stripping everything back to its bare bones, and I felt like that would be predictable."

"FROOT" encapsulates her intentions for the record in a neat five minutes and thirty seconds. "When I wrote the song I literally felt like I was ready, that I am in my prime and I feel like as an artist I've grown. I feel fully realised as an artist, and in my own identity."

Diamandis mentions that "Blue" has a bit of a disco twang, and the same is clear on "FROOT". Alongside a '70s aesthetic, it's all forging towards a clarion theme. "Let's be honest, there's been a lot of disco around over the past year," she says. "That's really interesting to me; whatever the zeitgeist is at the time, that always leaks into whatever else is happening music or popular culture. I'm not a huge fan of disco music, but it really felt right. I'd been working very closely with a bassist at the time, so when he provided that lick on "FROOT" it was very interesting. I can honestly say it happened in the most natural way possible, it wasn't like "let's make a disco record!" [laughs]. I guess whatever's happening in the wider culture it always leaks into what you're doing, it's impossible to avoid it if you're aware of what's happening around you.

"It's not all like that at all though! God, can you imagine me just doing a happy disco record?"

“When I was a 21 I was an idiot, I remember wanting Brody Dalle's voice so I started smoking and shouting all the time... but it never worked, and now I'm just stuck with a bad habit.”

On The Family Jewels, Diamandis cited the likes of Daniel Johnston as an influence ("His songs sounded like they were recorded in a cupboard") and so I ask who has been the inspiration for FROOT: "I love The Cardigans...[also] Brody Dalle in The Distillers... I think it was her third album, Coral Fang, that 'initiated' me. It's one of my favourite records ever. I've been obsessed with her since I was 21... I love Shirley Manson. I guess those sort of women are inspiring to me."

"Figuring that out becomes easier when you realise who you really look up to and relate to."

There's a discrepancy between Marina and The Diamonds and the kind of music that Dalle and Manson create. "That was a major factor in me making FROOT rougher sounding than my other records, Diamandis asserts. Will she ever push further along that road? "I don't think so. That time's gone. The window's closed. When I was a 21 I was an idiot, I remember wanting Brody Dalle's voice so I started smoking and shouting all the time... but it never worked, and now I'm just stuck with a bad habit. I think when you're young the image you have of yourself is sometimes different to who you actually are, so what you want to be is perhaps not what you are going to be. Plus, because I was really ambitious at the time, I saw pop music as a way to expand upon those desires and plans.

"I'm a huge pop fan, but it's more that those big influences are the earliest ones. When I started listening to music properly I was around 19 - I was quite late - and those were the big ones around at the time. People like Fiona Apple, Dresden Dolls who I really liked, The Distillers obviously and PJ Harvey."

FROOT marks a new chapter of Marina's life in almost every way imaginable, and Diamandis relishes the uncertainty that this new frame of mind will bring: "I'm used to planning everything to sweet fuckery, and I'm not planning anything this time," she says with a slightly nervous laughter.

"I'm just happy to let everything happen."