The same day, I wrote to my local council, Lambeth, to ask them to leave more verges unmown. Here is their reply:
When it comes to the management of verges on the public highway we have to... ensure grass and shrubs are kept short and tidy. This is because previous consultations with residents and other customers indicated that they preferred to see highway verges kept neat, tidy and well presented in order to create and maintain a clean, presentable image for the local neighbourhood. Although we receive regular enquiries about allowing some verges to be left to develop into rough grassland or meadows, we have to politely decline such requests and respect the wishes of the existing community, as well as to avoid difficulties in keeping them safe and free of litter, and in accessing them for regular maintenance.
I will publish their response again here when I get it. In the meantime, if you've ever rung your council or landlord to request that grass be more regularly mowed, please think of the bees and butterflies who depend on its dandelions and clover and daisies, and think twice.