Sometimes I find myself longing to write a self-help book. The most wonderful challenge is to write a self-help book about something you don’t know a thing about, such as: How to Survive as a Princess. Tip 1: Don’t praise your portrait straight away, even if you did study history of art at St Andrews. Follow your grandmother-in-law’s example: give a friendly nod but remain noncommittal.

David Cameron travels to the Netherlands to give a speech about Europe. It makes me want to write a self-help book about Europe: Europe for the British. Point 1: Germany is always the boss, except when it has just lost a war. Point 8: In case war does break out after all, keep Boris Johnson close at hand to sort things out.

I could write self-help books about things I do know about. I’m thinking of: Ten Ways to Avoid Having Guests and Avoid Visiting Friends. I don’t think it has a big potential readership.

But what is the difference between a novel and a self-help book?