Piers Jackson lies on the floor with his knees in the air and Jade Jagger sits on them. Jade, heavily pregnant, is wearing a brick dress, brick jacket with fresh daisy in the button hole, ruby cross round her neck, and bare legs.

The unmarried former wild child and daughter of Mick and Bianca Jagger has arrived to put the finishing touches to the exhibition she is having with Piers, the father of her child. But this won’t be the sort of exhibition a 20-year-old girl normally has after daubing for just three years.

Tonight 700 people have been invited to The Collection in South Kensington for the couple’s exhibition in the aeroplane hangar-sized Sir Norman Foster space, as they keep calling it, that used to house Katharine Hamnett’s clothes. Mick Jumping Jack Flash will be there and so too Nicaraguan Bianca, his sultry ex-wife from whom he parted acrimoniously. There will be the usual mix of aristos and rock stars.

Neither Jade nor Piers has had any formal art training. ‘I never wanted to go to university,’ says Jade, who was expelled from St Mary’s school in Wiltshire when she was caught cavorting with her then boyfriend Josh Astor, Lord Kagan’s illegitimate son who was convicted of drugs charges in 1989. Things are different these days. The couple work in the same room in a farmhouse in Somerset. (She is practical and methodical – ‘I just treat it like cooking’ – and he spends more time being cerebral and squinting.) They regard painting as a contemplative, meditative kind of art. ‘It’s like yoga,’ he says. ‘It gives us a stability and balance in our lives.’ Today they are each showing 10 paintings. ‘I’m a Libran, it has to be perfectly balanced,’ says Jade. But yesterday at 4pm the paintings, which should already have been hanging, hadn’t yet arrived.

‘Who put the carpet down?’ wailed Jade, looking across the sea of exhibition felt that covered the space. ‘We want it removed. Tell them it’s . . . it’s a fire hazard,’ she laughs, full of joy and jokes. Expecting her first baby in June, she bends over and pulls up a strip of carpet. The couple, who have been together for three years, met in Florence in 1988, when she was 17. They were both studying Renaissance art at the time. ‘It’s always been a dream of mine to start a family,’ she recently told Hello! magazine. ‘Motherhood is a very strong instinct within me and the primary inspiration for many women . . . One day we would like to marry.’ We sit on the floor to talk, because there is only one chair. A little later the paintings arrive. ‘Hey! That’s wild. They’re quite strange these frames,’ she says, seeing them for the first time. Mid conversation, she sets to with paint stripper. ‘The artist has to have the last word,’ she says, erupting in giggles and rubbing the frames.

Jade has striking looks, lovely legs, a high forehead and the sort of lips that people pay money to have made with collagen. Known once as an outspoken and temperamental wild child and shopaholic, she is actually serene and down to earth. Piers is the more dishevelled, cosmic and intense of the two. He has propensity for facial shadow, hiking boots, T-shirt and blue trousers. Friends say he has been a calming influence on her. So what is it like to be a wild child who has settled down into a quiet painter’s life? ‘I think my early image was one that the Press created. If there was any rebelliousness in me, it was no more than the average young person,’ says Jade. ‘Those daring headlines were just daring headlines.’ She admits she has changed since meeting Piers, becoming a painter and settling down. ‘Since becoming older. I’ve changed, of course. We put a lot of emphasis on our home life, domestic life, cooking and families,’ says Piers. He also thinks her work has changed since she became pregnant: ‘It’s got better, definitely.’

They don’t compete in the work space. ‘I’m not a competitive person at all,’ says Jade. Piers then talks about energies and a spirit inside him, saying that competition doesn’t let the right things out.

Similar in style, their figurative paintings are oils inspired by the couple’s travels in Nicaragua and India among other places. Colourful, simple and decorative, they are of landscapes and people. They took from two weeks to two months to paint. ‘They’re not named,’ says Jade, ‘so we can’t really talk about them.’ Piers, 22, says they’re inspired by Gaugin, Matisse, Vouillard and Bonnard, and they are numbered one to 20. A man walks past with a 4ft piece of primed hardboard covered with a stripe of sea, a stripe of red rock and a stripe of blue sky: a Minorcan scene. ‘The ones you want to keep, you put a big price on,’ says Piers. ‘And the ones you don’t like, you hope they sell,’ says Jade, who adds that she always felt a bit nervous about parting with her creations. They are selling for an average of £2,000, and Minorca is their most expensive painting. ‘They’re for people to enjoy, like a nice carpet,’ says Jade. ‘I don’t mean a wall-to-wall one.’

Do people pay heed to her art because of her name? Or is she talented in her own right? ‘To be honest, I think we paint attractive paintings. Obviously we get more attention because of who I am. But if people want to buy them for the wrong reasons, that’s their problem.’

But would she prefer to be recognised in her own right? ‘I don’t know. It isn’t possible to hypotheticalise (sic) about what it would be like to be someone else, because I’m not.’ She adds: ‘I’m not that keen on the attention.’

Jade’s parents encouraged her. (‘My mother was more protective, whereas my father was keen that I wasn’t too sheltered,’ she told Hello!) ‘They’ve been very helpful. Being artistic people, they have been more understanding than other parents might be. And obviously financially it was much easier to start off with support,’ says the daughter of the man who is reputedly worth £75 million.

She used to sell flowers by Portobello Road to supplement her income. Does she aim to become financially independent with her paintings? ‘Well, I’m not financially dependent on my parents.’ That laugh again. Would she like to be a famous artist? And where can she see herself in five years time? ‘We’re just country folk,’ she says, in a country bumpkin accent. ‘Yes. London’s too distracting,’ explains Piers. ‘Because a lot of our friends are young too and they don’t all have jobs.’

Another journalist arrives, stiff in navy suit. ‘I’m saturated (sic). I can’t think of another word to say,’ says Jade.

‘You haven’t said anything for 20 minutes,’ says Piers.

‘I know. I’m gawping at my work,’ she replies. With admiration? She laughs. ‘With horror and fear.’