LONDON - Pop star Prince had fashionistas dancing in the aisles at London Fashion Week on Wednesday when he staged a surprise performance at Matthew Williamson's catwalk show.

The singer, who is playing a series of concerts in London, at first appeared to be only a front row guest at Williamson's spring-summer 2008 collection.

But the usual fashion scene became a pop concert when a Prince track struck up and the first two models onto the catwalk -- a pair of identical twins in purple dresses -- started to dance.

Prince, wearing a black suit and hat, then began singing into a microphone from his seat before jumping up and performing on the runway flanked by his band.

By that time, many in the audience, who included actress Trudie Styler, the wife of musician Sting, were on their feet clapping and snapping photos with their mobile phones.

"He really wanted to do this, and you don't say 'No' to Prince," Williamson told Reuters TV after the show, his first in London since he left for New York five years ago.

After the impromptu gig, Williamson, who is in London celebrating his 10 years as a designer, sent models down the catwalk in richly embroidered skirts and dresses glittering with seed pearls.

Striped jackets -- a theme throughout London Fashion Week -- were offset with splashes of turquoise, pink and orange.

The show closed to the strains of Prince's "Kiss" from his best-selling 1986 album "Parade."