Alex Garland smiles broadly only once while in my company, and it’s when I’m about to leave. As I put on my coat and say goodbye, an irrepressible and unmistakable grin of relief spreads across the film-maker’s face. I don’t take it personally – and Garland is unfailingly courteous throughout our conversation – but this seems indicative of both his serious character in general, and his uneasy mood at present. I wonder if it is partly due to filmgoers like me, with our insistent (mis)interpretation of his work, that Garland says that his latest film will also be the last he directs.

And what a way to go out. With a rumoured $50m budget, Civil War is the most expensive film ever made by indie production house A24, and on an…