Neiman-Marcus vice president Marilyn Kaplan spent last Sunday checking out the young designers' stalls at the Olympia exhibition center here and taking in a couple of fashion shows as well. At the end of the day she told her colleagues she would walk home alone.

Two hours later she found her way back to her hotel. "I've made a big decision," she recalled thinking to herself. "I'm going to double the amount of money we're spending in London."

That's the way a lot of people have reacted to the spring collections shown here over the last five days. "What is happening here is today's version of the Youthquake," Kaplan explained, "with endless fresh options for self-expression. I'm very taken with it all -- I make no bones about it."

Not since the 1960s has there been so much interest in London fashion. Close to 10,000 buyers from all over the world descended on London last weekend -- nearly 3,000 more than last year -- to check on the progress of some familiar name designers and to scout new ones. They weren't disappointed.

"We've got a lot of art colleges that produce a lot of fashion designers," said designer Wendy Dagworthy at Monday night's official government party at Lancaster House, a London mansion. Dagworthy, 34, has been designing for 11 years. "When I started it was expected that a recent graduate would work for someone else," she said. "Now they want to work for themselves."

"Education gives kids the freedom to be original," said Jean Muir, for years one of London's top designers, who was made a C.B.E. (Commander of the British Empire) for her work encouraging young talent.

On the opening day of the London shows, 52 designers -- all sharing models and shoes and hairdressers -- presented a sampling of their creations in a cooperative effort sponsored by Challoners, a local employment-agency chain. There was hardly a consistent theme in the one-hour show, but there were a lot of spontaneous ideas from such labels as Wet, Gusto, Bazooka, Relief, XLNT and Imprint.

No one is inhibited about trying anything, said designer Liza Bruce, "because no one has much to lose." Her designs include black, white and orange American-flag tops, cutout layered-knit swimsuits and dresses in fabrics from the space program. The motto of her company is: "If it doesn't sell . . . oh well."

"Since we have nothing to lose, we let all of our ideas come out. Why not?" said the designer, who has a tiny dollar-sign tattoo on one temple. "Individuality is our most important search."

Jane Foster and Patrick Gottelier, whose knitwear labeled Artwork is sold at Woodward & Lothrop, think the fashion world's focus on London is just a matter of it being London's turn. "The focus has been on Japanese designers, and before that New York or Milan or Paris . . . This is our moment," said Foster, admittedly pleased.

It was the miniskirt that brought many buyers to London 20 years ago, but they aren't finding a preponderance of them now. While short skirts were a favorite theme with the Italian designers who presented their collections in Milan a week earlier, long, easy skirts showed up far more frequently here than minis.

Many of the styles shown by designers interpreted the looks popular on London streets, particularly the big shirt that kids are wearing, often with only one tail tucked in.

And often the clothes expressed a reaction to established trends. Since prints haven't been used in years, many designers are showing them here, as did the Italian designers and as the French undoubtedly will next week in Paris. In London, however, the prints are often created by artist friends of the designers rather than by the big textile houses.

In contrast to the current concentration on natural fibers such as cotton and wool, many of the designers here are seeking the "sleazy" synthetics last popular in the 1960s. When Commander Salamander's Stuart "Izzy" Ezrailson spotted some polyester print shirts in a stall at the Olympia, he told his wife Wendy, "It's garbage. I love it."

While most French designers are hardly frightened by the young upstarts across the channel, Jean-Paul Gaultier, for one, admits that he goes frequently to London to get ideas.

Even French President Franc,ois Mitterrand is taking a cue from London. Last season, British Prime Minister Margaret Thatcher invited the entire fashion crowd to 10 Downing Street for drinks. This year, when the buyers and press arrive in Paris Wednesday night, they will find an invitation from the President and Madame Mitterrand to the Elyse'e Palace to honor the designers and to celebrate the opening of the spring shows.