“What do you mean, you’re my daughter?” Paul asked, when Catherine called him.

“My mum went to a fertility clinic and was given donor sperm, and it’s yours,” Catherine said.

“Oh. Yes,” Paul said, bewildered. “I did go to a clinic with my wife. We had infertility problems. We went to Wanstead clinic.”

Suddenly, Catherine understood. Her biological father had been another of Boyd’s patients. Paul and his wife Jane (whose names have been changed for this article) had had private fertility treatment at his east London clinic in 1969. Paul’s sperm had been checked. Somehow, the sample he gave was used to create Catherine.