UK narrative non-fiction is where research has to behave like story. It can run through history, science, memoir, reportage, nature, or cultural criticism, but agents are looking for scene, shape, and authority rather than a pile of interesting facts. The proposal has to prove the book can move.
This UK page shows agents who explicitly represent narrative non-fiction. The broad search toggle catches more who'd consider it under history, memoir, biography, essays, popular science, politics, or cultural writing.