The greatest hurdle for anyone who sits down to write a sex scene is the knowledge that your mother is going to read it. Or your father, your colleagues, the other parents at the school gate and probably, one day, your child. I pity my son in this regard; I’ve managed to reach my 40s without ever acknowledging that my parents know anything about sex, so I can only imagine the level of discomfort I would feel if my mother had ever committed anything explicit to print.