The nuts and bolts securing your tender sides to the base are an important factor which marks the tender as fairly early .. it is using what we have come to term "Nut and Bolt" manufacture ... this is important when you look at the history of Hornby in the early years ... Frank Hornby of course made his mark early on with Meccano , the English variant of your yank Erector sets ( and yes Hornby was first lol! )
Meccano was of course a construction kit , and building off the success of that, Hornby went into model train manufacture , the very first set made by Hornby was indeed a construction model of a train, yep you could disassemble and reassemble it yourself , but rather than cobbling it out of crude Meccano , Frank Hornby custom made the locomotive and tender bodies and chassis's in tin, which the new owner could then use as a very presentable and fully functional model train .. naturally this involved using nuts and bolts to join various sub assemblies .. thus the Nut and Bolt construction locos and tenders ... it wasnt until a few years later that Hornby utilised tab and slot lithography to cut down on manufacturing cost and sell completed model trains ready to run which were not easily pulled apart 
Nut & Bolt Loco and Tender .
under cab view showing nuts and bolts which hold the chassis onto the cab body , even the motor was held in by Meccano nut and bolt ( very bottom of pic )
and the very first prototype built entirely from Meccano by Frank Hornby to give him the idea
