A painting by Boris Johnson’s mother, Charlotte Johnson Wahl, is among the works in a fascinating new exhibition at Bethlem Museum of the Mind

Seven years ago, London’s Mall Galleries were presented with a proposal for a major retrospective. No one on the selection panel had ever heard of the artist, Charlotte Johnson Wahl, but when told she was the mother of the then mayor of London, Boris Johnson, its members suppressed a collective sigh. I know, because I was one of them. We assumed, unfairly, that anything with the name Johnson attached to it must be a vanity project.

But then the images flashed up on the gallery whiteboard, and our assumption was quickly demolished: the paintings were clearly the work of a serious artist with an original vision. In any case, she was only a Johnson by marriage to her first husband, Stanley. By birth the artist was a Fawcett, daughter of the eminent jurist Sir James Fawcett, one time president of the European Court of Human Rights, and granddaughter through her mother, Beatrice Lowe, of two American liberal academics.