Four afternoons a week, I pick up my three-year-old son from nursery. The stroll home takes us past six restaurants, three bars, a dry cleaner, an off-licence and two charity shops, one of which, in a stroke of merchandising genius, displays toys and children’s books at knee height in the window. Walking past is not an option. We both spot it at the same time: a copy of Julia Donaldson’s 2001 classic Room on the Broom.

It’s a hardback. In Donaldson land, that means a first edition. I flip to the copyright page and check the printer’s key, which rises in odd numbers from one to nine, then falls in even numbers from eight to two. Better still, it is a beautiful copy. I suspect it has never been read, and certainly not by a grubby toddler. All children’s books here cost 50p. We add a few toy cars to bump us over the £2 card limit and proceed home, bargain in hand.

In January it was announced that Donaldson had supplanted J K Rowling as the UK’s all-time bestselling author. Her books have sold 48.6 million copies. Given their larger-than-average size, put end to end those books would, by a back-of-the-envelope calculation, stretch from London to New Delhi and back again. This