LONDON (AFP) - British designer Vivienne Westwood transformed the catwalk into a protest march at London Fashion Week on Sunday, blending style with politics and sharp tailoring with anti-austerity placards.

The long-time rebel and activist held the launch of her spring-summer 2016 runway show for her Red Line collection in the basement of the University of Westminster.

As fashion writers and celebrities took their seats, the lights went down and the sound of a siren announced the show had begun.

A group of people took to the floodlit catwalk holding placards reading "Climate Revolution", "Austerity is a Crime" and "Fracking is a Crime", referring to the controversial method of extracting shale gas.

"It's incredibly important... to be political because we face incredible danger from our politicians and we've got to stop them!" Westwood, 74, wrote in a letter given to each guest. "They cause climate change and war... they're taking us to mass extinction and we have to do something."

She seemed to have in her sights the Conservative Prime Minister David Cameron, an enthusiastic backer of fracking.

Just last week, she rode an armoured vehicle to his home in protest at the policy.

Her protesters brandished their placards outside the fashion show venue before she later led them onto the catwalk.

Her collection seemed inspired by activists.

Models wore draped and ruched clothing with a vintage, mish-mash feel, many with badges pinned on their lapels and their faces daubed with black paint.