Can a collective portrait of Britain hold together a country that feels as if it is splintering apart? That is the quietly radical hope behind Es Devlin’s new installation at the National Portrait Gallery: a living portrait comprised not of monarchs, politicians or celebrities but of thousands of ordinary faces drifting slowly into and out of one another. Created in collaboration with Google Arts & Culture Lab, A National Portrait for the National Portrait Gallery invites people across the UK to upload a selfie, which is then transformed into a portrait rendered in Devlin’s smoky charcoal-and-chalk style before joining a constantly evolving and revolving carousel of portraits projected on to a framed screen. The effect is strangely intimate: faces hover briefly at the surface before slipping away again; strangers fold into strangers; features surface and dissolve. Watching it feels less like looking at images than catching fragments of people as they pass in a crowd.…