Cosmetic surgery is a global growth industry and is now so advanced that there is virtually no body part that can't be remodelled. But why do so many people want to change the way they look? Susie Orbach is a psychotherapist and author. Thirty years ago she wrote Fat is a feminist issue, now she says we're all at risk of body insecurity and shame. Stephen Sackur asks her what will make us content in our own skin.