LUCIENNE DAY was one of the first British designers to become a celebrity. In the early Fifties she contributed to a BBC Radio series on design; her Chelsea coach house - done up in a glamorous modern style - was celebrated in a 1954 issue of House & Garden; the next year Day and her husband, Robin (a furniture designer soon to become famous), starred in a highly stylised Smirnoff vodka advertising campaign. Even her dinner recipes were published and slavishly copied in thousands of bright, young middle-class homes.

Thirty years before 'design' became a fashionable word in Britain, Lucienne Day was blazing a colourful trail for her youthful profession. After graduating from the Royal College of Art 50 years ago, she made her name and career with Calyx, a radical fabric design inspired by her painter heroes, Joan Miro and Paul Klee, and first shown at the Festival of Britain in 1951.

Nothing quite like this uncompromisingly modern pattern had been seen before. It was considered so daring, even by Tom Worthington, the adventurous design director of Heals who commissioned it, that Day was paid only half the normal fee. Worthington hurriedly paid the other pounds 10 when Calyx - catching the spirit of the times - instantly became popular at home and abroad, particularly in the United States.

In 1952, Lucienne Day won the International Design Award of the American Institute of Decorators, the first to be awarded to a British designer. Less than a year later, her abstract fabric, based on plant forms and making a bold use of colours (originally lime-yellow, vermilion, black and white, on an olive background) was being adapted and copied by companies at home and abroad.

Excited perhaps by the colour, excitement and availability of a new wave of fabric patterns after years of war, ration books and utility design, the British public - unable to afford Calyx at 28s 5d (pounds 1.42) a yard - rushed to buy second-rate modern glitz loosely based on the work of Day and her contemporaries. By the late Fifties almost every home in Britain had been affected by the radical spirit of Lucienne Day, albeit in bastardised form.

She herself went on to design altogether bolder and more abstract fabrics and wallpapers - mostly to complement the powerful new architecture of the Sixties. When country house style began to push the vestiges of abstract Modernism out of the popular design shops (John Lewis among them) in the Seventies, she gave up designing mass- production fabrics and moved into the world of one-off design.

Thrilled by designing cheap fabrics for a mass market in the middle and late Fifties (she says she got a 'great kick out of seeing my fabrics roll off the machine to sell at 10s (50p) a yard'), Day felt there were simply too many clashing fabrics competing for attention in the homes of Fifties Britain. 'A printed curtain that looks magnificent in an exhibition, with acres of space all around and not much else, can be reduced to a garish, overpowering horror in a 12ft by 16ft room that already contains a textured carpet, one or more patterned wallpapers and some chintz-covered chairs.'

She adds: 'Because I'm a textile designer, I don't feel in any way committed to using printed textiles in every possible place; rather the reverse. I would rather do without altogether in some places and use roller or venetian blinds and then be really generous with the curtains in one main room.'

Today, still working from the Chelsea home she moved into 40 years ago, Day makes what she calls silk 'mosaics' from hundreds and even thousands of pieces of silk. Conceived on a large scale, these are avidly pursued by private and public collectors; they also grace a number of public interiors. The best known of her works, at least for many shoppers, is Aspects of the Sun, a bravura mosaic, 16ft by 9ft, hanging in the coffee shop of the new John Lewis store in Kingston upon Thames, where it has been joined by a second, Islands. Day was a design consultant, with her husband, to the John Lewis Partnership between 1962 and 1987.

The first big show of her mosaics was in the Lyttelton foyer at the National Theatre in 1981. She sold three-quarters, and another show at the National in 1990 was even more successful. Among the buyers was the Victoria and Albert Museum, which regards her work as among the most important British fabric design of this century.

A typical Day silk mosaic is about 6ft by 4ft and might be made of up 6,000 patches of shot silk, sewn together by a team of assistants. Paper templates on which each design is based are left inside the silk, so the compositions, when finished, are truly a mosaic of overlapping and interwoven materials. Day works with Thai or Indian silk; her favourites are the vivid shot silks of Mysore. These feature two different colours, in warp and weft, and so shimmer with different colours depending upon how light falls on them and where the viewer of a mosaic is standing.

Day is keen to stress that this new wave of work, which began when she gave up designing mass production fabrics in the Seventies 'to make way for younger people', does not mean she has become a craftswoman. 'I'm a designer,' she insists, 'not a maker. I employ others to make the mosaics.'

As a designer, Day hardly lacks recognition. Awards had come her way early. In 1954 she won the important Gran Premio prize at the Milan Triennale for a collection of fabric patterns including 'Spectators'. This was a significant feat for a British designer, particularly at a time when the Scandinavians were picking up virtually every international design prize. The award helped her to sell her work throughout Europe, as well as Britain and the United States.

She was soon working with such important Continental manufacturers as Rosenthal Porzellan AG, for which she began designing patterns for Raymond Loewy's 'Service 2000' tableware, for the Rosenthal 'Studio Collection'. Rosenthal's faith in modern designers was repaid in several ways; by 1961, the avant-garde 'Studio Collection' accounted for 60 per cent of the company's production.

Meanwhile, in Britain, Day was designing wallpapers for Crown and increasingly abstract fabric patterns for Heals. The influences on her work included graphic artists such as the renowned American Saul Steinberg. A graphic approach to fabric patterns meant reducing the number of colours involved (between 14 and 20 in a traditional chintz) until she was working with just a simple, single-coloured line on a one-colour background.

In 1962, at the peak of her influence in industry, Day was made a Royal Designer for Industry (RDI), one of a select band of 100 British designers. She was only the fifth woman; Robin had been made an RDI three years earlier for his work in furniture. They are the only husband-and-wife RDIs.

Day, one of four children, was born Desiree Lucienne Conradi in Croydon in 1917; her father was Belgian, her mother English. She was educated at convent school in Worthing, before training at Croydon School of Art (1934-37) and then at the RCA. Her course was interrupted by the war, during which she volunteered for the fire service (she was invalided out).

Her diploma show at the RCA got off to something of a disastrous start when future husband Robin, helping with her stand, stepped off a ladder and on to the pots she had made. But it was the fabric patterns that really mattered.

Day taught design after graduating and toured Scandinavia - as every young designer at the time dreamt of doing - before being commissioned to design Calyx by Tom Worthington.

Her story has been a remarkable one: an inspired avant-garde designer who has brought her ideas into the high street; a British designer who, in the infancy of her profession, sold her work and exported her skills to Europe and the United States. Her work, from Calyx to her latest silk mosaics, remains vibrant and delightful.

As a designer, she has balanced art with commerce and made the avant- garde popular without ever having to compromise. She has led a charmed life, and deserves it.

'Lucienne Day: A Career in Design', 23 April to 26 June, Whitworth Art Gallery, Oxford Road, Manchester (061-273 4865).

(Photograph omitted)