Since 2010, the number of teenage girls referred to the Tavistock Gender Identity Development Service has increased by 5,000 per cent. Now former patients and staff members are speaking out. For me it began with a graph. In 2017, I was shown a chart of children referred to GIDS, the Tavistock and Portman Trust’s Gender Identity Development Service clinic in northwest London. Overall case numbers had risen – from just 72 in 2009-10 to 1,807 in 2016-17 – but there was something more puzzling. Female referrals, once a fraction of males, now made up 70 per cent: from 32 to 1,265. The number of teenage girls with gender dysphoria (ie profound discomfort with their biological sex) had risen by 5,000 per cent in 7 years. My journalistic curiosity was sparked, more so when I could find no mention of this in the mainstream press. The only people collecting data and testimony were online parents’ groups in Britain and the US. Moreover, their stories revealed a distinct pattern, repeated worldwide from Australia to Sweden.