Every year, thousands of British children are conceived with the help of donor sperm. But few ever meet their siblings...

Caroline Pearson, a podcast producer from London, was a few days into her maternity leave when she discovered that her unborn daughter had two sisters. She had visited a website a friend had told her about, which allows recipients of donated sperm (such as her) to search for families who have used the same donor. If they’ve registered with this website, they could be anywhere in the world, since the US sperm bank chosen by Pearson and her husband, Francis, ships internationally, and the website, Donor Sibling Registry (DSR), is also US-based with an international reach. Pearson couldn’t resist, and typed in the donor’s reference number.

“Suddenly, I was overwhelmingly curious,” Pearson says. She didn’t expect to find anything – let alone two families living within a half-hour radius. The first profile was a single mother to a two-year-old girl, living nearby in London. It seemed an extraordinary coincidence. Caroline was “totally giddy”; her partner Francis, a photographer, was cautious. “I tried to rein things in,” he says. “Caroline was pregnant and we were already dealing with becoming parents, and the donor process. But all this other stuff, it was so unknown. I’m practical and you think: yes, that could be amazing – but what if they’re awful people?”