A surgeon friend told James Caspian that in one year he’d performed two reverse gender reassignment operations on patients who’d swapped gender then changed their minds. “This is new,” he said. “Someone should research it.” Caspian, a psychotherapist at a private gender clinic, discovered no one ever had. So he enrolled on an MA course at Bath Spa University with the intention of writing his thesis on “detransition”.

No one could accuse Caspian, a slight, thoughtful gay man, of being hostile to trans people. He is a trustee of the Beaumont Trust, a gender educational charity, and in 16 years as a counsellor had hundreds of patients who, after working through childhood and emotional problems, concluded that “changing their gender presentation makes them more free