WHEN FASHION is soft, the twinset returns to favour. This summer, the classic combination of sweater and cardigan is experiencing a new lease of life. The twinset is as integral a part of the season's wardrobe as floaty dresses and layers of linen.

Why do twinsets seem so thoroughly modern? Perhaps it is because they hover between the classic and sporty: a flexible outfit for an age when the rules on what to wear and when are becoming blurred. Christa Worthington's book, Chic Simple: Clothes (to be published by Thames & Hudson on July 5), is full of level- headed wardrobe advice, and makes the point that twinsets - also called sweater sets - are versatile garments, easy to dress up or down to fit the occasion or the mood.

Coco Chanel pioneered this form of dressing during the First World War, when she sold jersey dresses with matching jackets, and cardigan-style suits, to wealthy holidaymakers in Deauville. But it was Pringle, a knitwear firm in the Scottish Borders, that developed the twinset as we know it today. The inspiration came from Otto Weisz, a refugee, designer and artist from Austria who joined the company in 1934 - a radical move at a time when manufacturers simply did not employ full-time designers.

Weisz was convinced that a knitted garment was intrinsically more comfortable than anything that could be woven. Knitwear, he argued, naturally follows the contours of the body, and the wearer benefited from the elasticity of natural fibres. Pringle's original twinset was a knitted crewneck and cardigan, but now just about any two-piece knitted combination is given the name.

In the Fifties, the twinset was adopted by Hollywood's film stars, who did a neat promotional job for the Borders firm in the process. They draped the cardigans around their shoulders and wore them with a glitzy brooch or string of pearls.

In the Pringle archives, the company proudly keeps a letter from Deborah Kerr, whose films include Quo Vadis and From Here to Eternity, telling 'how tremendously admired my Twin Sets have been here in Hollywood, not to mention how useful they have been to me personally.' The new twinsets are lighter and softer than ever. And there is definitely nothing twee about them. Cream-coloured layers in increasingly light-weight knits make the twinset a practical wardrobe option for summer, even in warm weather.

Although the quality of their product has never been in doubt, the knitwear manufacturers of the Borders are showing great improvements in design terms. At the top end of the price range, Ballantyne Cashmere has come up with twinsets in everything from knitted silk to superfine merino and cashmere. Next summer, the company is adding cashmere-cotton and cotton-silk style, which will bring down prices and make the knitwear even cooler.

Pringle is selling extra-fine cotton twinsets this summer, with the cardigan priced at pounds 58 and the sweater selling for pounds 40. The colours of the Fifties are also popular, particularly pretty pastel pinks and blues. Shapes are loose, but never baggy. Even at its most relaxed, the twinset should never be sloppy.

Oyster knitted silk twinset: cardigan, pounds 170, and sweater, pounds 128, by Ballantyne Cashmere from Harrods, Knightsbridge SW1; Ballantyne Cashmere, 153a New Bond Street, W1; raw silk trousers, pounds 195, by Katharine Hamnett, 20 Sloane Street, SW1; silver beads, pounds 275, and bangle, pounds 150, by Jacqueline Rabun from Jess James, 3 Newburgh Street, W1; Space NK, 41 Earlham Street, WC2

(Photographs omitted)