This solemn group of posters teaching safety to British citizens comes from the archive of the Royal Society for the Prevention of Accidents. The images are from the Wellcome Library's website; I first saw them on the blog the Passion of Former Days.
The RoSPA displayed a series of its 20th-century posters in a 2012 exhibition, after rediscovering a small archive of them in an outbuilding. In the exhibition notes, RoSPA curators noted that the society, which dates back to World War I, focused on road safety and pedestrian awareness in the 1920s and 1930s (much like analogous American safety organizations).
In the 1940s, wartime conditions, the RoSPA curators wrote, "made industrial safety a matter of national survival," and the society worked with the Ministry of Labour to produce and disseminate posters designed to minimize workplace accidents. Most of the posters below, designed by artist Leonard Cusden, are from this period and are aimed at factory workers.