Tanya Sarne won the loyalty of thousands of women as the designer behind Ghost. Now she's set to reach a new audience with a range for John Lewis. She tells Carola Long about her breezy approach to dressing

Oh, but you must try it on," says Tanya Sarne, as she shows me designs from her new 30 piece capsule collection for John Lewis. About three seconds later – these really are clothes one can slip into – and I'm in a little Thirties-style cropped jacket in aubergine satin. Undeniably perfect for concealing less-than-toned arms, it's the kind of piece Susannah and Trinny or Gok Wan might hail as "problem solving," yet looks like a sweet floppy vintage jacket that Kate Moss might wear to a wedding. "I thought it's a perfect cover up for a wedding or dinner," confirms Sarne, "I can see a younger woman going for this, while an older woman might choose the version with the frill."

Sarne, who founded Ghost in 1984 sold it in 2006, and started her current label Handwritten last year, is so keen for me for me to try the collection because her design philosophy is as unashamedly about comfort and ease as it is about high fashion. In fact, these dresses are so fluid and the fabric – which is the same unique material that Sarne has used all her career – so breathable, that Monica Seles used to practice tennis in a Ghost dress.

Sarne's success has been built on what many of her devotees might declare a miracle fabric. She uses a type of viscose that initially resembles a stiff net curtain until it is boiled, dyed and shrunk to about a quarter of its original size, when it takes on the appearance of vintage crepe. It has a natural stretch that fits women of all shapes and sizes from the very slender to the heavily pregnant particularly well, and, crucially for any busy woman, can be "thrown in the washing machine." "They are also perfect for travelling," she adds, "because you can roll them in a suitcase then just give them a bit of a shake or get rid of any slight creases by hanging them in a steamy bathroom." This instantly recognisable fabric became the foundation for Ghost.

Under Sarne's leadership, Ghost had an almost cult following. Ghost shows – and parties – were a highlight of New York Fashion Week, where Naomi Campbell and Helena Christensen would appear in her shows as favours, in return for clothes.

Rumoured to have provided some of the inspiration for Edina in Absolutely Fabulous, Sarne's biography is overflowing with drama and glamour. A former model – now in her early sixties she is still strikingly beautiful with blonde curls, olive skin and sultry, kohl rimmed brown eyes – she married the arthouse film-maker Michael Sarne, with whom she travelled the world. Their circle of friends included Jack Nicholson and Roman Polanski.

When Sarne split up with her husband, she has said, the catalyst for founding Ghost was the imperative to "feed the kids and pay the rent." As such, she understands the need for fashion to be practical and, one of her favourite words, "multifunctional." "I'm not an Alexander McQueen or Vivienne Westwood," she says, "You wouldn't wear the clothes I make to the Oscars. I try to make clothes that are multifunctional for women of all ages, shapes and sizes. Wearable, good quality clothes. For me John Lewis is about quality and I wouldn't have done a collaboration like this for anyone else." The fabric is made in the same family-run Italian mill that Sarne used to create her first collections in the Eighties and the designs evoke the soft, ultra-feminine, often Thirties-inspired shapes that she is best known for. Highlights include a loose painter's smock, wide pyjama style trousers, tea dresses and mock wrap dresses, while the range also includes slip dresses and strappy camis.

Sarne's talent as a colourist is apparent in the romantically muted – and flattering – shades of aubergine, orchid (a dusky rose colour) and alabaster. "Pantone has nothing on me," says the designer, whose hobby is painting. Forthcoming colours for her designs include a "sea foam-y green," and a, "lovely earthy sage," carmine and an inky blue for autumn.

Jo Hooper, head of womenswear buying at John Lewis notes that some of the designs don't look overly striking on the hanger but that they come alive when worn. Similarly, such simple silhouettes will benefit from clever styling, and allow the wearer to add their own touches. Team the wide trousers with a thin black knit and a long necklace, and – voila – Ginger Rogers-style pyjama dressing. Throw the aubergine tunic over denim shorts or cigarette pants, add a patterned cotton scarf, and you have the kind of low key chic that would work everywhere from Notting Hill – where Sarne lives – to Salisbury, where she often spends weekends. She designed the collection to appeal to, "the smart, stylish women I see shopping in John Lewis in Salisbury. They are incredibly well-dressed women with style and elegance, but not in thrall to super high fashion. They are busy, independent women of all ages." And for once, all ages means all ages. Sarne recounts a letter from a woman who had read an article saying that she made clothes for women up to the age of 70. The letter-writer said, very indignantly, that she was 80 years old and still wore Ghost. "That's the kind of thing I want to hear," says Sarne.

Tanya Sarne for John Lewis is available in 10 stores nationwide, for information call 08456 049 049