Daddy's girl: Simone Rocha

It should probably come as a surprise to learn that John Rocha loves fishing – after all it's not exactly a standard fashion industry hobby. However Ireland's most famous fashion designer, who is celebrating 25 years of his label, is so calm that it's easy to imagine him sitting on a riverbank staring serenely into space.

And it's not just the Hong Kong-born Rocha himself who's remarkably peaceful. With its white walls, sculptures and shelves piled with art books, his shop in London's Dover Street, where we meet, has the still atmosphere of a particularly cutting-edge Bond Street gallery.

Rocha's 23-year-old daughter Simone combines this inherited calmness with a more excitable, youthful enthusiasm, as she explains how she's following in her father's footsteps and becoming a designer. She showed her MA collection as part of the Central Saint Martin's College show at London Fashion Week in

February, and wants to set up her own label. She's planning to produce the collection in Ireland, at her father's studio, and in August some of the pieces will be available in the shop.

Simone Rocha's collection is based around tailored pieces in black and white, but while sheer panels add a lighter edge, the collection is harder and more minimal than her father's aesthetic. John Rocha's tailoring tends to be fluid and loose – more ethereal than sharp.

"I think Simone's view of fashion is quite different to mine in that there is a more youthful element, and it's more edgy" says her father, now 56. "But I can see the understanding of fabric, which I suppose is what I do as a designer. So you can see a certain DNA there."

Perhaps the aspect of Simone's collection that is closest to her father's designs is the headwear. She says, "The collection was quite tough so I thought it would be nice to have something soft and romantic." The wire structures draped in net were inspired by Papal hats and by a mourning tradition in the Aran Islands, whereby bereaved women wear petticoats on their heads. Simone grew up in Ireland, but left after she completed a four-year degree at the National College of Art and Design in Dublin, to study at Saint Martin's in London. She says she is now looking at her home country for inspiration.

Growing up in Dublin, which Rocha made his adoptive home after moving there from Hong Kong in the late Seventies, Simone admits she didn't see her father's career as exotic.

"Not really," she says in her warm Dublin accent, "There wasn't that kind of glamour to it. It was great fun you know, they had all these creative friends, photographers, artists, and there was always something going on, lots of music. But at the end of the day, it's mum and dad and they are still giving out to you about what time you come home." "Mum" is Odette, John's friendly wife who is in the shop downstairs, wearing a draped, black silk design from the spring/summer collection. Simone says that among the highlights of her childhood were the frequent journeys abroad, as Rocha combined travel with research.

His method isn't as direct as heading off to a country then coming back and basing a collection around it, however. Instead, he says, "I always listen to my subconscious when it comes to travel. It opens your mind and lets you see things in a very different way than the internet and magazines."

Twice a year, Rocha goes back to Hong Kong to see his family – six of his seven siblings still live there. His children (he has another daughter, Zoe who is 27, and a son, Max, who is 20) accompany him every couple of years, and have seen the two-room apartment where the seven siblings grew up.

"It's the size of this room, maybe a bit smaller," says Simone, gesturing around a minimal white meeting room above the shop, "and the beds come out of the wall. It has given us a sense of who we are and where we came from. My dad is the hardest working man I know."

Hard work has taken Rocha from his small Hong Kong flat to the status of renowned international designer, recipient of British Designer of The Year in 1994, a CBE and a stalwart of London Fashion Week, where he shows regularly. He came to Britain to work as a psychiatric nurse, but when he met a friend who was a fashion designer he thought, "I can do that myself. It seemed an easier, more fun thing to do. It was the Seventies, all peace and love."

He studied at fashion college in Croydon, "discovered Irish fabric" while on holiday in the Republic, and was sponsored by a mill in Ireland which provided the fabric for his final collection. Instead of chasing passing trends, Rocha has forged a signature style of romantic clothes with craft detailing. "I am a great believer in natural fibre," he says. "The foundation of my career is about beautiful linen and handcraft. It's my ambition to bring handcraft into a modern form."

Rocha was the second designer to create regular collections for the Designers at Debenhams range, after Jasper Conran. At the time, such a collaboration between the high street and a high-end designer was unusual, but now Rocha believes that without the support of the high street, many designers would be unable to survive. "I don't see fashion as an elitist thing," he says. "For me it doesn't matter whether something costs £5 or £5000, as long as it's done well." In addition to clothes, the Rocha.JohnRocha range includes bed linen, china, childrenswear, watches, bags and shoes.

Rocha is hugely prolific. He launched the John Rocha at Waterford Crystal collection in 1997, and will continue to create the range under the company's new owners. He collaborated on the Dublin hotel The Morrison, and has designed residential flats in Liverpool, Birmingham and Budapest.

Surprisingly, given his romantic style, his broad oeuvre doesn't include wedding dresses. "It's too nerve-wracking," he explains, "because if anything goes wrong you will ruin the big day." He did make his wife's dress though, for their marriage in 1990. It was in "ivory silk, 1930s-ish". He adds that he couldn't possibly do without Odette's female perspective: "You do need someone whose opinion you trust because it can be quite lonely. You can't make every decision yourself."

There is one thing that Rocha always does without Odette – and Simone – however: his beloved fishing. For that he has fishing friends, in Cuba (where he catches bonefish), Russia and Ireland. Along with his passion for collecting art – his spring/summer show was inspired by the Irish-American painter Sean Scully, whose work he owns in addition to pieces by Picasso, Francis Bacon and Matisse – regular fishing holidays help clear his mind and keep him enthusiastic after more than two decades.

"If I didn't have a break after each collection I don't think I would be as excited about fashion as I still am," he smiles.