An important collection from the wardrobe of one of Hollywood's most striking style icons is coming up for auction. Rachel Shields enjoys a preview

Her chic black dresses, big sunglasses and elfin elegance made her an instant – and enduring – style icon. For more than 50 years women have copied Audrey Hepburn's look, but next month fans will be able to get their hands on the real thing, when the actress's clothes go under the hammer in London.

The most coveted items in the 36-piece collection are two gowns made by the French designer Hubert de Givenchy for the actress's screen roles: a black silk dress worn by Hepburn in the 1964 film Paris – When It Sizzles, and a Chantilly lace cocktail gown worn in How to Steal a Million in 1966, which are expected to sell for at least £15,000 each.

Also on sale at Kerry Taylor Auctions on 8 December are dresses dating from 1952 to the late 1960s, including the wedding dress made for her planned marriage to James Hanson – which she called off before the ceremony – and the Elizabeth Arden dress the actress wore on the night she met her first husband, the actor and film producer Mel Ferrer.

"She loved fashion, because in many ways it was about playing a role," said Sean Ferrer, Hepburn's son. "But being appropriately dressed was the most important thing for her. That's why she gelled with Givenchy; she didn't like to be flashy. She would rather be underdressed than overdressed."

The actress had a clause inserted into many of her film contracts that she would only be dressed by the designer. In 2006 the black Givenchy dress worn by Hepburn in her most famous role – that of the eccentric socialite Holly Golightly in Breakfast at Tiffany's – sold at Christie's for £467,200, more than six times the expected price of £70,000.

"She was absolutely connected with Givenchy, who was just at the beginning of his career," said Rosemary Harden, of Bath's Fashion Museum. "His dresses showcased her, and they will have an enduring appeal."

The collection, which is owned by the Austrian fashion designer Tanja Star Busmann, a friend of the late actress, also includes hats and belts, and a selection of letters in which she discusses filming Roman Holiday and her planned wedding to Hanson.

The auction is expected to attract a high-profile bidder in the shape of Victoria Beckham, who has received an early edition of the catalogue. A self-confessed fan of Hepburn, Beckham has reportedly spent £250,000 on letters from the actress to her father.

Kerry Taylor, who will conduct the sale, said: "I've been getting calls from everyone, from housewives to young women. Men are interested, too. She is a bit of a gay icon.

"It is a difficult collection to value. The value of an item depends on a number of factors: how beautiful it is; if it is by Givenchy; if there is a picture of Audrey in it; if it appeared in one of her films," she said.

Half of the proceeds will go to the Audrey Hepburn Children's Fund joint venture "All Children in School", which aims to educate 120 million children worldwide.