@Don McErlean Nice pickup !
That unit is , I believe, actually a Whistle Station/Controller !!!
comes from the later plastic loco set "Battery Operated Figure 8 Train Set with Smoke Whistle and Trestle"
https://spur00.de/nomura Scroll down to the bottom
But in related Fatman news ... I also picked up another French Hornby carriage , this one from a 3-rail electric set as it has a pickup shoe fitted ( I think this is a factory kit option for lighting the carriages )