They might actually have been Dorman and Smith
(borrowed from wackypedia)
Made by Dorman & Smith Ltd. (using patents applied for in 1943) the plugs and sockets were rated at 13 A and were one of the competing types for use on ring final circuits. They were never popular in private houses but were widely deployed in prefabricated houses, council housing and LCC schools. The BBC also used them. Some local authorities continued to use them in new installations until the late 1950s. Many D&S sockets were still in use until the early 1980s, although the difficulty in obtaining plugs for them after around 1970 often forced their users to replace them with BS 1363 sockets. The D&S plug suffered from a serious design fault: the line pin was a fuse which screwed into the plug body and tended to come unscrewed on its own in use. A fuse that worked loose could end up protruding from the socket, electrically live and posing a shock hazard, when the plug was removed.