I meet Martin Creed more than a week before his retrospective What's the point of it? opens at the Hayward. The gallery is full of 25 years' worth of improbable, witty, uplifting art; I am especially gladdened by a wall covered in 1,000 prints of broccoli.  But the show is not ready yet: the atmosphere is of playful disarray. There is a display case in which there is a crumpled sheet of A4 paper (a 1994 Creed provocation). On top of it, someone from the gallery has placed a sticky note that warns ART WORK! – to passing cleaners. One of the things that makes Creed controversial is that he does not draw a line between art and life. He says: "Anything is art that is used as art by people."  All in black, he has the look of an unaccountably cheerful mourner. He has a bowler hat, moustache and glasses that look like stick-on props, as if he were only disguised as himself, trying on his identity. And this is fitting because trying it on – and out – is at the heart of his work. He is lightheartedly and profoundly experimental. "It is a matter of seeing how it goes," he says. He was born in Wakefield, in 1968, but his father (an ironmonger who used to lecture on glassmaking and jewellery at Glasgow School of Art) moved the family to Scotland when he was three.  For all his humour, there is no mistaking the anxious underlay in Creed. He likes to sample colours, order things, override any pressure to choose. Yet he longs to defeat this compulsion: "One of my big problems is about control – I am trying to bypass that." He finds artistic decisions easier than ordinary decisions.  Creed is also an original, minimalist musician – his grandmother was a concert pianist. "I was taught as a child the most important things were music and art." He has a starkly entertaining CD, Mind Trap, coming out, an ambitious ballet piece and a brave composition, commissioned to celebrate the Royal Festival Hall's newly restored organ – his duet will explore the "inhuman" organ versus a hand-held harmonica.  When he won the Turner prize in 2001 for Work No 227, in which lights went on and off in a room, someone threw eggs at the walls. Creed is easily hurt: "I go between thinking my work is shit and that it is great." And what about the exhibition's title: What is the point of it? Whose question is it? "It's mine." But isn't it ours as well? "Oh, aye," he says.
The Turner prize winner tells Kate Kellaway about the point of a piece of A4 paper and broccoli on the eve of his Hayward retrospective