Two pictures below of the Hindle-Smart Electric Articulated Lorry, both the unboxed no. 30w, a trade box model, all maroon, until 1954, and the subsequent individually boxed no. 421 in maroon with red hubs. The cast in number 30w was changed too by deepening the die over there, resulting in an oval in relief showing 421.

Thirteen years ago there was a discussion on the talk model toys forum, which I will not copy here but just refer to: 

http://www.talkmodeltoys.com/discus/messages/27668/1190.html?1345308081