<p>Reputation for frumpiness is over as M&S wins over younger audience with shows at Silverstone, Ibiza and now LFW</p><p>This autumn’s London fashion week boasts plenty of familiar labels, from Burberry to Alexander McQueen, ready to show off their wares. But on Wednesday there was an unexpected addition: Marks & Spencer is joining the luxury lineup.</p><p>The British high-street retailer will celebrate its 100th anniversary in the fashion industry by staging a catwalk show in Septemb