Everywhere you look – from Donald Trump railing against Mexican immigrants as ‘rapists’ and ‘criminals’, to Australia’s own bipartisan and uniquely draconian system of offshore detention – Cuarón’s bleak, cinéma-vérité vision of a perpetually grey-skied Britain that denies entry to refugees and dehumanises those already there, seems to have been mistaken for a how-to guide rather than a cautionary tale.