I’m sorry for anyone who went to the Chelsea Flower Show on Thursday. My own visit was paid on Wednesday evening, when a golden sun still dipped SW3 in honey; the dry spell had gone on for so long that we all took it for granted. Driving through Sloane Square the next day, my youngest son wondered why some people were ‘wearing plastic bags’.

They were Chelsea refugees, in rainwear handed out by a sponsor; billowing sheets of rain had gusted all day. Water pooled in the streets. Those tangles of seemingly self-seeded flowers in the show gardens must have been knocked flat.

To city dwellers, the rain came as a relief. London has always been a dusty city. To Dickens, the airborne particles might have been ‘mummy-dust, dry atoms from the Temple… loosened grains of expression from the visages of blunt-nosed sphyxes’.

The dust heaps at King’s Cross became a central image of Our Mutual Friend-although his Victorian readers may have understood dust as a euphemism for other kinds of organic matter. In Paris, you have to skip as the water cart passes, threatening to drench your shoes. Hydrants are turned on and the gutters cleansed. In London, choked with the fluff from plane trees, we must wait for rain. How good the air smells when it comes.