ACE Callsender
One of the chaps I work with at the Dean Forest Railway found this in his garage. As far as we can tell, it’s a callsender for generating simulated traffic in a telephone exchange. We don’t have any more information than that at this stage, and would really like a schematic or even just a pinout for the connector! If it can be made to do loop disconnect dialing (which somehow given its age I doubt) it might even be useful!