The ballad of the billionaire

Kirsty Bertarelli is an intriguing conundrum. The 38-year-old Staffordshire-born former Miss UK is, according to the Sunday Times Rich List, the richest woman in the country. She is married to Ernesto Bertarelli, a Swiss pharmaceuticals entrepreneur, and together their fortune is estimated at £5.95 billion. They live between Geneva, Knightsbridge and Gstaad, are very active philanthropists and have three young children. And yet here I am, at Edinburgh Castle, waiting for Kirsty to begin her set as the support act for Simply Red frontman Mick Hucknall. She soon appears, brightening the drizzly evening in a one-shouldered silver minidress with matching shiny ankle boots. 'I am so happy to be here!' she shouts, before breaking into the title track from her new album

By rights Kirsty should be on a superyacht cruising exclusive turquoise waters, but instead she is shimmying about the stage with a guitarist in a kilt. When she sings 'Black Coffee', the song she wrote after first meeting Ernesto, which All Saints recorded and which went on to become a number one hit, she beams with delight as the audience wave their hands in time to the melody. Among them is her husband, sitting near the stage in a crisp blue shirt and cargo trousers, taking photos on his phone and punching his fist in the air.

Money can buy many things, but it cannot buy a good voice, natural exuberance or charisma. Kirsty has all three. Her voice is strong, big for her petite frame, although it can also be breathy and intimate. She writes good solid pop music. But still, one can't help but wonder, why is she doing all this?

'When you have a passion for something, when you are very creative, you can't just let go of it, it is always there,' she explains over a Caesar salad and Coke earlier that day. Her accent is a melange of Euro VIP and Chelsea girl. She is tanned and fit, in faded jeans and a cream vest. Her twinkly blue eyes have a hint of mischief to them and she laughs easily. She is neither grand nor distant, although a Swiss PR man called Paco does sit with us, silently, for the duration of the interview.

Kirsty Roper, as she was then, was born in Oulton, Staffordshire. The youngest of three children, her father ran the family ceramics firm Churchill China. 'I had a very rural childhood, with a beautiful home and loving parents. We had a tennis court and played tennis all the time. We all had horses, although I wasn't as good at riding as my sister.' Kirsty's passion was for music and performing; her mother is musical, and together they would do amateur operatics. After O levels at Howells boarding school in North Wales, Kirsty decided to pursue a career as a singer-songwriter, dabbling in modelling to pay her way. She was as surprised as anyone when, after her agent entered her for Miss UK aged 17, she won the competition and went on to come third in Miss World in 1988. 'I'm quite proud of it, but I quickly realised being a beauty queen wasn't something I wanted to do,' she later said.

Armed with her victory tiara, she moved to London, to a bachelor-girl mansion flat off Park Walk in Chelsea, bought for her by her parents. She had a busy King's Road social life, a BMW convertible, and a habit, upon making new friends, of reading their future in their palms and writing poems about them, which she would then present to them. 'I was always very creative, I always kept diaries. I was interested in writing down people's stories when I met them. I used to love writing those little poems. It is just an interest in people, a sort of a connection really.'

Kirsty sees this as the genesis of her songwriting urge, and while she still did a bit of modelling on the side, her energies were devoted to making music. 'I was going round different studios, not particularly nice ones, just desperately trying to get a contract, to make a success of myself. I was always writing lyrics on anything I could find: napkins, bits of paper, cigarette packets.' By the time she was 24 her father's company had gone public, and Kirsty was bought a house in South Kensington and given a £3 million trust fund. Still, she pursued her chosen career and began working with the DJ Gary Davies, recording in a makeshift studio – a bedroom with mattresses pushed against the walls. A recording deal with Warner was in the offing, but then something happened that both kick-started and stalled her recording career. Kirsty met Ernesto Bertarelli.

Ernesto's family firm, Serono, was founded in 1906 by an Italian, Cesare Serono. The pharmaceuticals company was initially run, and later bought, by Ernesto's grandfather Pietro and subsequently taken over by his father Fabio. Ernesto was born in Rome, raised in Switzerland and gained an MBA at Harvard Business School. His father died prematurely, of cancer, in 1998, leaving Ernesto, aged 32, as owner of the company (he had been made CEO in 1996) and he spent the following decade capitalising on his father's legacy, turning Serono into one of the world's most successful biotechnology companies, doubling the yearly revenues to over $2 billion.

In 1997 Ernesto was holidaying off the coast of Sardinia, staying on his 128ft yacht Vava. At a dinner with friends, he was introduced to Kirsty, who was then in her late twenties and single after a two-year relationship with the conservationist Damian Aspinall. It was, she says, love at first sight. 'You know when you fall for someone, when you talk to them and you start to go red. I became very bashful and he had the same response to me. We only had eyes for each other.' Kirsty returned to London and spent two weeks staring at her phone. 'I was hoping he would call and thank God he did.'

Falling in love with Ernesto inspired Kirsty to write 'Black Coffee', the lyrics charting the narrative of their romance: Night swimming/Beach walking/Always silent/Never talking/Then you call my name/And I know inside I love you – and then later – Daydreaming/Chain-smoking/Always laughing/Always joking/I remain the same/Did I tell you that I love you? And while it must have been galling for Kirsty to see her words and melody turned into a vehicle for All Saints, she got her man. They married in 2000, in a marquee in Geneva, and in front of their 250 guests Kirsty sang 'Black Coffee'. 'I was elated that my song had been so successful, but it was a double-edged sword, and by singing it at our wedding I felt like I reclaimed it for myself.'

This would surely have been the time to forge a music career, to build on the international success of 'Black Coffee', but although Kirsty continued to write songs for herself and to put on impromptu performances for friends (Frank Sinatra tunes are a favourite), babies, and later boat racing, took over the Bertarellis' lives. The couple had three children in rapid succession, a girl and two boys. 'When you have a child you just want to devote yourself to them, all your energy and creativity gets poured into them. I was overwhelmed with my love for my children,' she says. And then there was the America's Cup, a highly competitive, wildly expensive yacht race that Ernesto's team, Alinghi, won in 2003 and 2007. He was the boat's navigator in 2003 and its afterguard runner in 2007, as well as heading up the team, and for three months in 2007 Kirsty and their family lived on Vava in Valencia. The project took up nearly ten years of their lives and the current hiatus is only because Ernesto is waiting for the 2010 champions, the BMW Oracle Racing team (backed by the American computer tycoon Larry Ellison), to dictate where and when the next race will happen.