By Rachel Sanderson and Cindy Martin

LONDON (Reuters) - London Fashion Week has always been a showcase for the weird and wacky, but Oscar-winning actress Emma Thompson suggested on Tuesday it should also learn to have a laugh.

"I'm all about bringing the smile back into fashion," Thompson told Reuters TV on the red carpet at the headline event of the fourth day of the fashion fest, the gala opening of an exhibition of haute couture.

"If you've got a posh frock on you've got to smile. When I've seen pictures of fashion week all the models look so miserable. Not their fault, but they all look a bit like they're in a bit of a sulk."

Thompson, who is one of Britain's best-known actresses and has starred in the Harry Potter movies, joined other stars of stage and screen, socialites and business tycoons for the launch of "The Golden Age of Couture: Paris and London 1947-1957".

Kate Moss and Quentin Tarantino, designer John Galliano and musician Prince were among those gathered at London's Victoria & Albert Museum for a fundraising event which charged 10,000 pounds ($20,000) for a table of 10.

The exhibition, which runs from Sept. 22 to Jan. 6, shows more than 100 dresses dating from the launch of Christian Dior's New Look in Paris in 1947 until the designer's death in 1957, by which time the great couture houses had become global brands.

Celebrating the end of war and the birth of a new era, the decade set a standard for dressmaking and high fashion under the auspices of couture houses Dior, Balenciaga, Balmain and Fath that has rarely been surpassed.

The couture gowns worn by the event's female guests -- many long and beaded in pale, creamy hues -- attested to that opulence and contrasted sharply with Tuesday's runway shows where "geek chic" starred for a second consecutive day.

Models at Paul Smith, one of Britain's bigger brands with an annual turnover of almost 200 million pounds ($400 million), sported stripes galore with loose jackets and long, baggy skirts and shirts with some tied at the neck in a large bow.

While none of the models looked particularly cheery, they did boast one feature Emma Thompson might enjoy -- chunky round spectacles perfect for Harry Potter.

London Fashion Week ends on Thursday.