Sienna and Savannah Miller design catwalk show

You had to use your imagination to see the influence of Joni Mitchell, Jack Kerouac and director Wim Wenders in the impressive catwalk show by actress Sienna Miller and designing sister Savannah Miller at London Fashion Week Saturday.

But those were the inspirations the unique designing team of Twenty8Twelve cited for their spring and summer 2011 collection, a focal point of Saturday’s shows on Day Two of fashion week.

The crowd at the Old Sorting Office in central London seemed to include an unusually high number of young blonde women who styled their hair exactly like Sienna Miller — blonde and slightly wild, often parted down the middle.

Even the models used the Sienna hairstyle and big sunglasses to give them the casual, glamorous look associated with the actress, who has starred in “Factory Girl,” “Layer Cake” and other major films.

Known for creating a sexy rock chick look, Sienna and Savannah Miller did not disappoint their fans, winning over the crowd with slinky mini-dresses, tight black cocktail dresses, and a series of jersey outfits, some with revealing cutaways.

They offered a slouchy, comfortable look. There was a denim minidress with pink frilly details at the bottom, like a puffed up petticoat, and some lovely lacework and antique embroidery embellished other outfits as well.

Still, it was difficult to see the “our girl in the Nevada dessert” theme mentioned in the sisters’ publicity package, although there were many earthy tones in the collection.

Afterward, Savannah Miller — pronouncing herself exhausted and ready to rush home and see her kids — said she took some of her inspiration from early color photographs by Paul Oterbridge from that remote region of America, and from the films and books that depict it.

“I just love the colors, it’s really nothing more than that,” she said. Their mission statement cited Kerouac’s landmark beat novel “On the Road” as a major influence, along with Mitchell’s “Don Juan’s Reckless Daughter” album.

Actor Jude Law, Sienna Miller’s on-again-off-again sweetheart, pronounced the show a success after viewing it from a front-row perch.

“I don’t know how she finds the time to do it, but she spends lots and lots of time designing,” said Law, who particularly admired a short black cocktail dress and another outfit that features a white shirt styled with a small cape on the back.

Some of the outfits were deceptively simple, like a plain white tee paired with blue shirts and an undecorated white, lacy minidress with a narrow black belt. There were a few denim shirts, suggestive of the American West theme.

The sisters drew heavy applause when they walked out hand in hand at the end of the show to briefly wave to the crowd.