French fancy: Sonia Rykiel

Sonia Rykiel is known as the queen of knits – and now she's brought her quirky Gallic style to the high street with a new collection for H&M. Très jolie, says Carola Long

As if Sonia Rykiel's bright, witty jumpers weren't uplifting enough, the French designer has come up with another reason to be cheerful. Thanks to her collabor- ation with H&M, we can all get our mitts on her knits for around a fifth of the price of her diffusion line, Sonia by Sonia Rykiel.

The collection focuses on knitted pieces in pink, black and yellow, and includes rhinestone-adorned jumpers, blazers, trapeze and tube dresses, leggings and dungarees. There are also accessories, such as patent belts and kitsch plastic bangles, as well as – quelle surprise – jaunty Parisian berets and childrenswear.

It's her first clothing collection for H&M following the lingerie range she designed for the chain last year, and handily bridges the gap between a winter wardrobe and shivering in new season buys.

However, not only are these instantly gratifying cheap-chic buys, they are also timeless. When I interviewed the flame-haired designer, who is now 79, at her St Germain apartment at the end of 2008, she said, "The clothes I made in 1968 can still be mixed with the clothes of today." Her designs don't change wildly with the seasons or follow trends, and her signature style is a playful mix of girlish and garçonne, served with lashings of Left Bank quirkiness and a colour palette of purples, reds, hot and pale pinks, yellow and of course, black. Rykiel's collections often feature tailored or harem trousers paired with sexy Seventies blouses, loose tunics or trapeze dresses, and, of course, knits decorated with anything from stripes to cherries, whorled corsages, rhinestones, slogans and trompe l'oeil designs. When Rykiel was described as one of the 10 most sensuous women in the world, she responded by putting her first word on a jumper; "sensuous". The influence of Sonia Rykiel's sweaters is all over the high street, which is currently in thrall to all things sweet and Parisian. Think Eiffel Tower designs and slogans such as "What's not to love?" – which appears on a cute, oversized sweater in Oasis. The most literal? A stripey Topshop jumper saying simply "Paris".

The appeal of Rykiel's clothes is that they are imaginative, sexy and fun – qualities that are reflected in the smiley demeanour of the models on her catwalks. She told me that she even encourages her models to look cheerful, by saying, "Smile, look happy, pick a man in the audience and look at him like this [ cue coquettish look]. You can have a conversation with your eyes." The eldest of five daughters in a Russian Jewish family, born just outside Paris, Rykiel was dubbed the "Queen of Knits" by Women's Wear Daily in 1968. She married a boutique owner in 1960, but after separating from him a few years later began designing maternity clothes and fitted sweaters, one of which appeared on the cover of Elle magazine. In May 1968, in the midst of the student riots, she opened a shop on the rue de Grenelle in Paris. "I opened it in the morning and closed it in the evening," she said. "It was close to the Sorbonne and there were students demonstrating everywhere. Then I opened it again two months later." The atmosphere on the Left Bank was "fun, mysterious, interesting, happy. There was something in the air. Paris was a melting pot. It felt like San Francisco had come to the Left Bank." Rykiel's boutique offered a fresh alternative to many of the more rigid designs of the time, and in the early Seventies she pioneered clothes with exposed seams, and no hems or linings.

Rykiel, who has posed for Andy Warhol and provided the inspiration for one of the characters in Robert Altman's film Prêt-à-Porter, has never stuck to fashion. Often referred to as a thinking woman's designer, Rykiel has published several books, including a novel called The Red Lips and a collection of fairy tales, and released a record with Malcolm McLaren in 1994. She has a dreamy, imaginative side. For her, knits are an artist's statement; a very French one. "They represent true freedom," she says. " A knit wraps and attaches. Every day it wraps its sleeves around my neck and we vow to each other eternal love! I love the idea of this game and this passion, hand-in-hand with H&M."

Rykiel has kept her business in the family and her daughter Natalie is president and artistic director. It was Natalie who organised the 40th anniversary show in October 2008, which ended with 30 models wearing Rykiel-inspired looks by renowned designers. Martin Margiela created a dress made of frizzy orange fur while a red-haired model sported a jumper dress with giant knitting needles by Jean Paul Gaultier. Natalie Rykiel says of the H&M range, "I wanted to get to the heart of the brand by offering a joyful 100 per cent knitwear collection." Fashion doesn't get much more feel-good than this.

Sonia Rykiel pour H&M Launches on 20 February