I'm interested to know to what degree the Big Four companies moved goods wagons belonging to other companies. For example, how often would you see, say, a LMS goods van as part of the stock being hauled by a GWR loco. If goods had originated in an area served only by one company would they be unloaded and loaded into another company's wagon at a "boundary" station or would the wagon simply be shunted into the other company's train?
I pride myself at being fairly competent at formulating complex Google searches but this has defeated me!
Thanks for any help you can give.