Daniel : What a great find, thanks for posting. You are right, the MO class of Hornby was O - gauge but a smaller scale than the rest of the line. I have one of the first passenger series of this line from about 1930-31. It is pictured below. Not nearly as sophisticated as yours but the MO line did get better as the years went on.
Daniel, as always, thank you for posting. I had never seen the "AD" set your pictured before.
Don