The great sperm heist: ‘They were playing with people’s lives’

For 40 years, Catherine Simpson thought she knew who she was: a nurse, a mother of three, a daughter and a sister. She looked like her mother, Sarah, but had the same temperament as her father, George: calm, unflustered, kind.

Then her father died. There was a dispute over his will, and that led her mother to call and tell her something that made the ground dissolve beneath her feet. George had had a vasectomy long before Catherine was born. She and her brother had been donor conceived in Harley Street using the sperm of two different anonymous men. George was not her biological father.

“In that moment, my brother turned into my half-brother. My grandma wasn’t my grandma. None of my dad’s relatives – people I’d been brought up with – were biological relatives.” It had to be a mistake, Catherine thought. But Sarah assured her that George couldn’t be her father. (The family’s names have been changed.)

Catherine didn’t know it yet, but this was the first revelation in what would become a decade-long search to find out...