All-American dreamers: this season designers have gone west for inspiration

Backstage at the Chanel spring/summer 2008 show, the designer Karl Lagerfeld is explaining the American Dream theme behind his latest collection for the label: "It was the inspiration of this famous couple, the Murphys, in Europe, Villa America, the house in the South of France," he says. "It was when Americans and Europeans were very inspired by each other, the days of Fitzgerald and Hemingway and all that. I think that was the best time ever."

Lagerfeld was referring to the 1920s, a moment in fashion when the Jazz Age expatriates Gerald and Sara Murphy represented everything that was elegant and exciting. Rich and glamorous, the pair helped to make the Riviera fashionable, rubbing shoulders with Pablo Picasso, Cole Porter, F Scott and Zelda Fitzgerald and Dorothy Parker. Lagerfeld's collection at Chanel updated their style – denim (surely the most democratic all-American fabric) cut into palazzo pants, trench coats and swimsuits worn with handfuls of costume jewellery – Sara is said to have worn pearls to the beach because "they wanted sunning". To emphasise his inspiration, Lagerfeld threw in a handful of Stars and Stripes designs (already a hit with Kate Moss and high-street retailers alike) and giant dollar-sign brooches.

Lagerfeld wasn't alone in his love-letter to America, with everyone, from Zac Posen and his take on Amish minimalism to Bernhard Willhelm and his Star-Spangled Banner dresses, looking Stateside for inspiration. It seems that, despite the present chilly political climate – the sub-prime mortgage fiasco and a heavy-handed foreign policy fuelling a global anti-Americanism – fashion designers (a perverse bunch at the best of times) have flipped out over all things American, sending out collections as diehard as Bruces Willis and Springsteen combined.

"For some reason, I always have an American inspiration in the summer and a European inspiration in the winter. I wasn't really conscious of this, but I think I connect America with summer," says the designer Peter Jensen, who is obsessed with old Hollywood, Wasp preppy style and old-school couture clients such as Lynn Wyatt. "There is something very upbeat and optimistic about Americana that feels right for summer."

Jensen's latest collection, called MINK, finds inspiration in the wonderfully wacky world of the film-maker John Waters, specifically the larger-than-life characters as played by the actress Mink Stole.

"Taffy in Female Trouble is a particular favourite," says Jensen. "I share the same obsessions as John Waters – suburban small towns, weirdos, black humour."

On this season's catwalk, this translates as cute pastel-coloured sportswear pieces worn with shiny patent loafers. "The Jock lettering came from the musical Hairspray – there's a character called Penny Pingle with a 'P' on her jumper," says Jensen. "It's made out of a patchwork of vintage children's T-shirts overdyed grey."

Jensen showed other felon-style grey outfits accessorised with police line-up ID numbers. The models' dishevelled hairstyles came from the same source, a book called Least Wanted – A Century of American Mugshots. "They're amazing," says Jensen, "especially the older ones, where the people have started out quite smart but then have got drunk or slept in a cell and look trashed but still really proud."

Acknowledging his dark sense of humour, he adds: "I'm interested in uniforms and clichés in dress in general, but especially in this show, I wanted to create a cast of characters. The playful, fun side is important to me – who wants to be depressed by fashion?"

There was an unmistakable playfulness in the minuscule pink silk prom dress that Jensen sent out at the end of his show. The look is already a winner. "I actually got an email from a girl in LA who wanted the dress to wear to her prom! And Rachel Bilson wore it in Nylon and loved it so much she asked to keep it," says Jensen. "I'm thinking I should start a line of prom dresses."

Although the collection appeared to be at the same time a comment on the sweetness and respectability of idyllic America and it's less than salubrious reflection, Jensen is not keen to intellectualise his work.

"It's much more juvenile and silly than that," he says. "If it is a comment on America, then it should be an amusing comment, not a political one."

Meanwhile, over at Pucci, the designer Matthew Williamson is having a Palm Beach-meets-Pocahontas moment. "I'm always influenced by travel and different countries. I felt it had been a while since I had referenced America," he says, "so I built the idea of a girl taking a road trip across the States, from desert to metropolis."

This meant a 1970s rich trippy- hippie look that referenced the jet- set style of Sharon Tate and Talitha Getty. "The Seventies are the best. I love the laid-back lounge styles and carefree attitude. It's always a cool, chic era to reference."

In his eponymous collection, which followed the same groove, Williamson threw in some colourful tailoring, a great traveller bag covered with faded tourist patches, and a handful of tie-dye scarves... Oh yes, and Prince, who caused a sensation at London Fashion Week when he opened Williamson's show.

"Prince's stylist called in some pieces for one of his shows, then we received a call saying he would like to perform and film it for his music video about his new muse, the model Chelsea Rodgers," explains Williamson. "The perfect way to celebrate my 10th anniversary."

Does the designer think that, having shown in New York for several years now, some American style may have rubbed off?

"I think it has helped me to define my creative identity more, and develop more diversity in my collections," he says.

Of course, some designers have Americana hard-wired into their style DNA. Francisco Costa, creative director of Calvin Klein, may have been hired to take the brand into the future, but the latest collection undoubtedly reached back to the archive for inspiration, channeling Klein in his 1970s heyday.

"Yes, the easy pleated trousers with bodysuits, the simple silk bias dresses, and the colour palette all have an American sensibility," says Costa. "The collection referenced iconic imagery that really speaks to the legacy of the brand and the house."

There can't be much in fashion that is more American than a nude, elongated T-shirt dress. "But for me," says Costa, "the nude colour is reminiscent of the desert and the West, and the shape has been updated with a seamless shoulder construction in a very technical fabric, all making it more than just a basic T-shirt dress."

While Costa offered an overtly modern collection of stylish and comfortable clothes, it is still possible to detect a touch of Claire McCardell and Mainbocher, two pioneers of American style, in the mix. "Always," says Costa. "McCardell made American fashion desirable, Mainbocher's creations represent American luxury."

And what is Costa's own American dream? "Not to sound clichéd," he says, "but as a Brazilian, I really feel that I am living my American dream."

There can be few designers who are more American than Ralph Lauren. Celebrating 40 years in business, Lauren, who has built the foundations of his brand on traditional American style, has been named an official outfitter for the 2008 US Olympic team. He will design outfits for the opening-ceremony parade in Beijing in August that will, "reflect the heritage and sensibility of the 1920s and 1930s, with a tailored and modern silhouette"; a sketch on his website hints at a nostalgic Chariots of Fire look.

Norman Bellingham, chief operating officer for the US Olympic Committee, says: "Polo Ralph Lauren is a quintessential American brand that represents a timeless and classic look."Curious, then, that for spring/summer 2008, the year of his Olympics presence, Lauren's collection that was all upper-crust Britishness. His show, with its floral tea-dresses, striped blazers, racing silks and toppers, was a homage to Ascot (through the eyes of Cecil Beaton in My Fair Lady), proving that, wherever our roots may be, our dreams are elsewhere.