Why do you say it's "rather overlooked as an early noir." The understanding of film noir as dating before Stranger and Screaming is already very well established, in the US as well as France and the UK.
Pick up any book with a filmography of British noir and On the Night of the Fire is listed:
John Grant's A Comprehensive Encyclopedia of Film Noir
Michael F. Keaney's British Film Noir Guide
Spencer Selby's The Worldwide Tradition of Film Noir
Andrew Spicer's European Film Noir