Do you want to know why Sam McKnight is the most succesful hair stylist in the world? It is not down to his sharp scissor skills or his way with wigs. It's his voice-deep and rumbling and sultry, with the softest of Scottish lilts.Which is exactly what you want to listen to when you are having your hair fussed over for three hours. Or when you are gettng a steak attached to your head (as he did for Lady Gaga to top off that meat dress). 'We had to shove it on with kirby grips' says Sam, 58. 'It was like a Damien Hirst installation-flies everywhere.' After 37 years in the business, not much shocks him. He's worked on more than Vogue covers, done Kate Moss's hair 'thousands of times' (including for her wedding' and travelled as Diana, Princess of Wales's personal hair stylist for seven years-he was the one who persuaded her to slick back her short crop. Downtime is spent pottering around his flourishing north London garden, where he grows tulips, roses, peonies, rhubarb.. Know why they grow so well? Because of that voice. He talks to them too.