As far as I know, there are two different castins for the boy of this bus, both are based on the Leyland STL. The chassis are the same for the two models.
The earliets bus does not have a roof box, it has small front windows and ridged hubs.
The later has a roof box, larger front windows and ridged or spun or plastic hubs.
This model was a promotionnal distributed by both Chloride Batteries Ltd. and Meccano Ltd. at least 100 000 were made.