Ellie Goulding has been working up a sweat. Her first single, 'Under The Sheets' back in the winter of 2009, introduced to the world a pop singer-songwriter, with a touch of the shy girl next door about her. Ellie was all dewy eyes and languid hair, as if she had emerged straight from English suburbia. And there was a hint of Kate Bush about the music, which mixed synth-pop and folk in a tasteful balance.

Appearances can be deceptive. Across the past year and a half, Ellie has sexed-up, toned-up and grown-up. Starry eyed ingenue no more, Goulding has morphed into something far more interesting and impressive: a pop glamazon who makes smart and sultry feel like reverse sides of the same coin. Shall we count the ways in which our girl has changed? Let’s start with the midriff – the seventh wonder of pop, it's so flat as to be virtually concave, an attribute which, judging by recent photoshoots, she believes it her duty to display at time she chooses. Which is a lot (good on her). Plus, there’s the hint of a properly steamy love life. Having dated a sensible British radio presenter for 18 months, her rumoured latter-day romantic entanglements have included – and this, we allow, is true only in the overheated imagination of celebrity correspondents – a dreadlocked DJ, a boy band pin-up and a ginger sexpot. According to the newspapers, she’s living the dream, in the fast lane with the hood down.

Her music, too, is fleshier as well as flashier. ‘I Need Your Love', Goulding’s 2012 collab with Calvin Harris, is the EDM banger you could bring home to your cool friends; ‘Burn’, her fi rst No.1 hit, updated Ibiza dance music for Gen Twitter; both exuded immense sex appeal.

All of a sudden, her star fi rmly in the ascendant, Ellie Goulding is one of the world’s biggest pop stars. Sales of her second album Halcyon are climbing inexorably towards the million mark in the UK. It has just reclaimed the No.1 spot in Ireland. She is due to play The O2 here at the beginning of March. If you’ve been on board from the start, part of you can’t help wondering: how the hell did all this happen? The curious thing is that, exactly the same thought goes through Ellie's mind.

“I never wanted to play arenas,” she says, taking time out to speak exclusively to Hot Press on a rare morning off (she’s just returned from her ritual visit to the gym). “I specifically said at one point that I wouldn’t do arenas. Then, the demand for shows kept getting bigger and bigger. Tickets would sell out really quickly. People who wanted to see me wouldn’t be able to come. You start to think, ‘Well, maybe I should play arenas'.”
And so you do...

How wrong can you be? Any impression of Goulding as a privileged child of affluent suburbia, a la the divine Ms. Bush, was completely misplaced. She is, rather, a self-created phenomenon who dragged herself from the often dark depths of council estate England. Clarinet was her fi rst instrument, taken up as a child, before she started to learn guitar at the age of 14. Highly intelligent, Ellie did well enough in school to go to university.

It was there that she started to realise her musical potential. She entered a college talent contest and did enough to impress Jamie Lillywhite – the son of producer Steve Lillywhite – who decided he wanted to manage her. A roller-coaster ride was starting, which would see her garnering immediate attention, winning the BBC's ‘Sound Of’ poll at the start of 2010.

Her obvious talents as a musician and a singer and the critical recognition notwithstanding, she suffered bouts of self-doubt and wasn’t quite clear how she wished her career to proceed. She had her dark moments, wondering if the hard work was worthwhile.

All of those doubts have since been thoroughly swept away. The success of Halcyon – an album that introduced the public to the concept of Goulding as sizzling pop tyro – has radically recalibrated her idea of who she is and where she fits in. She compares herself to a sullen adolescent blossoming into adulthood.

“I’m coming out of my teenage phase – the angst, the shyness, the insecurity," is how she puts it now. "If you perform for as long as I have, you inevitably gain confidence. My belief in my self has gone up loads.”

There is a price, she acknowledges. In 2010 Hot Press and Goulding had lunch together in Dublin: no one gave us a second glance. Now, paparazzi flock to her like mayflies. A few days ago, Goulding went for a drink with Ed Sheeran – they’re just friends, for the record – and pictures of the two exiting a bar were soon pasted all over the internet. A similar drama unfolded last year when she crossed paths with One Direction while touring the US: straight away, the Twittersphere was burning up with rumours of a romance with Niall Horan (again, strictly a friend zone thing).

“I’m very good at shrugging it off,” she says of her reputation as a man eater. “I laugh – even if it’s an embarrassing story." It's said with a smile. "Me and my friends will see the funny side. In the papers, I’ve never got stuff printed that was bad to the point where I’ve been upset. Usually it’s not true anyway – so there’s no point in worrying.”

Yes, but does she ever wonder – why me? She isn’t the only pop star with nice hair and a flat tum. And yet the media seems far more interested in what she gets up to after hours than Rihanna, Beyoncé and Gaga put together. The way the gossip press reports on her romantic entanglements, you'd imagine them public property.

“I makes no sense at all,” she laughs. “Honestly, I’m quite boring. This is a source of constant confusion. I suppose people are fed celeb stuff all the time and are conditioned to believe that the people they read about live amazing lives. It’s not true (laughs). I live a really mundane life.”

She admits that she didn’t see the apparent obsession with her love life in the UK media coming at all. Granted, Halcyon is essentially a break-up album, chronicling the end of her long-term relationship with DJ Greg James (a parting deemed so significant to the hoi-polloi it made the front page of the Daily Mail). But plenty of artists have released breakup records. She’s the one who's been singled out for special attention.

“It’s a source of entertainment, isn’t it?” she muses. “It distracts us from what really matters in our lives. That, fundamentally, is why people are interested in me as a tabloid case-study. You just have to have a good sense of humour and get on with it.”

The one 'high-profile' relationship she has confirmed was with Skrillex, the American EDM star, who comes complete with crusty-ish dreads. From the outside, it seemed that being in the orbit of the outgoing Floridian (real name Sonny Moore) sparked something in Ellie. She changed her hair; ditched her occasionally mumsy dress sense for something more daring; and generally started to act like a mature, rock 'n' roll adult.

She also had her first acquaintance with the sharp end of the showbusiness media as she and Moore briefly became a celeb couple, treated by the tabloids like the Posh and Becks of EDM. Confronted with a whirlwind of media prurience, Goulding responded in the healthiest way possible – with good natured bafflement.

“Celebrity couple – oh, don’t say that,” she instructed me in 2012. “We’ve never asked for any attention. We never tried to get attention. We don’t like to be photographed together or anything like that. It’s not something either of us initiated. People have for some reason taken a big interest. It’s one of those things that you shrug off and carry on. My focus is on my album and on performing and becoming a great artist.”

And on that front, she has been making giant strides.

Born in 1986, Goulding grew up on a council estate in Hereford, a glum town near England’s border with Wales. Its rock ‘n’ roll history is patchy, though it did give the world the glam rockers – revered by Def Leppard, among others – Mott The Hoople. She has described herself as the product of a broken home – her father walked out on the family when she was five and they remain estranged to this day.

Early in her career she talked freely about her difficult upbringing – recounting that her mother would blame herself for raising a son and three daughters in a single parent household, and speaking of the pain she felt, knowing she and her dad would never have a normal father-child relationship.

Nowadays, she is more circumspect. She recognises that she was naive starting out, and that placing her personal life in the spotlight hurt her family. At the same time, she wouldn’t change anything. She had her reasons for saying what she said: Goulding needed to get it out there before anyone else had the opportunity. She was determined to own her sadness. It was her story, not the media’s.

“I wanted people to know my background,” she explains. “My mum understood that. I was mistaken all the time for a student of [Amy Winehouse/Adele alma mater] the Brit school. Which I absolutely am not. Also, I was mistaken for coming from a privileged background, which, again, is absolutely not the case. I came from a council estate. At a young age, I decided I wanted to speak well. For that reason people have judged me differently.”

If you want to know what she thinks today about her father, she says, listen to her music. She put all her feelings into the song ‘I Know You Care’, a fan favourite from Halcyon. The title is ironic – in truth, she doesn’t think her father cares that much at all. Goulding wrote the ballad for herself, presuming it would be an obscure album track that not many people would focus on. Then Halcyon became a surprise international smash and, as a result, she finds herself singing it, night after night, to ever vaster crowds. No wonder her relationship with the tune has changed fundamentally: it doesn’t feel that ‘I Know You Care’ or its sentiments quite belong to her any more.

“It was very cathartic when I wrote it,” she proffers. “Today, I don’t have any bitterness or anger. I’m a really peaceful person. To me, that song is now a performance. There’s a little bit of the original emotion in it, of course. However, it’s not all there. Otherwise, to do it every night would be quite exhausting, I think.

"At the start, I thought: 'nobody is going to hear this'," she muses. "Lately everyone has talked about it more and more. It’s out there in a big way. I’m glad about that.”

She’s always been open about being a driven personality. Talking to me in 2010, in what was her first Irish interview – it took place the day after she was named winner of the ‘Sound Of’ award – the picture she painted was of someone who had decided, at a young age, to transcend her modest origins and make something of her life.

“I continuously did my own thing and always have done from when I was very young," she explained. "I studied for my GCSEs and A-levels and my degree and my music all by myself. I guess I was on my own journey. That’s how it’s always been – and that’s how it’s been up to the present day.”

Goulding, you will have gathered, is not a typical celebrity. She isn’t above enjoying the trappings of her status – and why should she be? Last year, there was a big to-do when she had a wild night out with Bjork (an avowed influence) and sundry chums in Costa Rica. Things turned so raucous that the group was politely asked to leave by management (boo!). At the same time, she’s extremely self-aware and seems to recognise that, dazzling though it may be, fame is ultimately empty, that pursuing it for its own sake leads only to heartache and ruin.

More than that, she’s quite careful in her relations with the media. Maybe it’s a product of having been interviewed approximately one zillion times since 2010, but she's very measured. She’s friendly, chatty even. But she doesn’t gush – everything is on message. Goulding knows what parts of her life she wishes to share with the world. That’s what you’re getting – nothing less, certainly nothing more.

That she knows what parts of her body she wants to share, and how, is also obvious. Goulding’s curves were on prominent display in a a recent issue of Marie Claire UK, where she posed essentially in the nude, only a few carefully placed hair strands preserving her modesty. Some pop stars participate in stunt shoots and end up looking grim and uncomfortable. Goulding, on the other hand, was absolutely at home having a camera linger over her – and it showed.

“It was exciting and surreal," she says. "They could have put anyone else on the cover. They chose me. I’ve seen a few photos of myself and thought, ‘Oh Christ’. When a photo-shoot comes out like that one, you’re really pleased. The truth is that anyone can take a good photo. I’m not a model, I’m a singer. However, it’s undoubtedly the case that, if you have a certain amount of confidence, you can pull off those photoshots. You can tell when someone is ill-at-ease or lacking belief. I was absolutely confident.”

Do photographers or stylists ever try and push her in a direction with which she isn’t comfortable? It’s all very well Marie Claire cajoling her into some tasteful near-nudity, but not everyone would be so respectful.

“Back in the day, I’m sure I did photoshoots I wasn’t comfortable with,” she nods. “I have a lot more control now. I do what I want. Anything I wouldn’t be into, my team wouldn’t even bring it to me. It just wouldn’t come near me.”

Having spoken to Goulding on several occasions, I can vouch for her charm. The only time things got a bit terse was at the tail end of 2011, when it seemed she had a shot at the UK No. 1, with her John Lewis-approved tilt at Elton John’s ‘Your Song’. As it transpired, she was shoved aside by the anti-X Factor Rage Against the Machine campaign, but with the prize still in sight she did a round of interviews. Before the tete-a-tete, I was told that under no circumstances would Goulding discuss the Royal Wedding, at which she had been after-dinner singer of choice. And so it proved.

“I had no right to talk about it,” she says today. “I was just performing, it wasn’t my wedding. It’s their life. I didn’t have permission to go around yapping about it. I will say it was a beautiful night and that they are wonderful people. It was definitely surreal – it was a strange situation to find yourself in.”

She has, meanwhile, chosen her musical cohorts carefully. Two years ago she toured with Katy Perry (they recently reunited for a duet of ‘Strong’ at a charity show in LA); and in 2013, she returned to the US with Bruno Mars. Clearly she has no problem with the word 'pop'.

“It’s hard to stay introverted if you’re hanging around with a massive superstar,” she told me last year, reflecting on her friendship with Mars. “Your self-belief is going to grow. You pick stuff up from watching people. Bruno is such an amazing showman. You think, ‘Hey, I should do some of that’. You learn from those around you. I have definitely got more confident. On the other hand, if it’s a small audience, I still come down with nerves. I did this gig recently where it was me and my guitar and I was terrified. It was like going back to an open mic night.”

She looks back on those early days, when she materialised at the centre of a fair-sized cloud of hype, with an air of wariness. With the BBC ‘Sound Of’ prize in her back pocket, the expectation was that she would be the perfect synthesis of edgy artist and commercial star. Quicker than you could say ‘inevitable backlash’, the UK media had the daggers drawn. Her debut album Lights was not especially kindly reviewed, and at the time Goulding’s confidence took a wobble.

“It was such a relief when the album got to No. 1,” she told me. “And if you think about it, isn’t that a horrible thing to say? I should have been delighted. It should have been a moment to savour, a fantastic surprise. Instead, my response was: ’Well, thank God for that. I’ve shown them, I’ve justified myself '.

“Journalists don’t want to be seen as being seduced by the buzz. They want you to think they’re ahead of the curve. With a lot of the reviews, I think they knocked a star off, simply because I had received so much exposure. The guy in The Guardian... I don’t think he’d ever written a review like that before. He seemed more concerned in writing about the hype than about me.”

Four years on, it’s fair to say that sniping by critics is no longer a concern. A global pop star, there is little need for her to be bothered with such trivialities. Following her chin-wag with Hot Press this morning, she has three photo-shoots to attend. After that, it’s off to Germany for a private performance (she won’t say who is hosting it, so we’re going to assume it’s an EDM-themed birthday party for Angela Merkel); a few days later, she’ll be in America promoting ‘Burn’, which is getting a big push there having shot to No.1 in Ireland and Britain last autumn. All of that, mind, is a mere preamble for her upcoming arena tour which begins on the Continent and swings through Dublin next month.

Goulding is looking forward to what will undoubtedly prove the busiest year of her career so far. By the same token, she’s experienced enough to know that what time off she has is to be savoured. As soon as she’s finished with her media obligations today, the plan is to switch off her mobile, decouple from the Twitter machine and kick back in front of her favorite TV show, Geordie Shore.

“It’s the equivalent of junk food,” she giggles. “It’s nice to have it as a treat every now and then. I mean, sure I watch films, read books. However, there are times you want to do something that’s absolutely not productive by any means. I like Geordie Shore and My Big Fat Gypsy Wedding in particular because they give me a glimpse into lives that are quite different from mine. I don’t go clubbing – in a way, I’m quite jealous of those who get to live normal lives. So I like looking at other people’ s situations – to get a glimpse into a world that’s completely different from the one I inhabit.”

Ellie Goulding plays the O2, Dublin on March 1. Her album Halcyon is on Polydor.