The Antique Partnership has dated this piece to the 1900s.
There are four holes in the base where the box was mounted on the running board. The interior shows signs of oils toos having been stored within.

The step inset is made of an early form of rubber matting and is original. The hinges are of substantial brass as is the lock and escutcheon which is secured with tiny brass screws. The exterior of the box is covered in a thick very dark paint which is as expected chipped and scratched but again is original.
50 cm wide 26 cm deep and 27.5 cm high
The Antique Partnership has dated this piece to the 1900s.
You can view the stock and full dealer information on the The Antique Partnership Profile Page