Bestsellers are different from fast sellers, cult favourites or the brand known as “instant classics”. They bear no relation to those books we call “the canon”, such as Pride and Prejudice – which became a “bestseller” relatively recently, when it was remodelled as chick lit. The term has become a slippery one and is often used to describe the thing it’s not. Most of the books promoted by Waterstones as bestsellers are nothing of the sort. They don’t come close to the sales figures required (4,000 to 25,000 copies a week in hardback). Bestsellers are not simply the summer’s top beach reads; they are cultural phenomena, and we like to think that they come, like J K Rowling’s Harry Potter and the Philosopher’s Stone or E L James’s Fifty Shades of Grey, out of left field.