GWR TPO circa 1915

An illustration from The Wonder Book of Railways of what looks like a Great Western Railway travelling post office. I can see no specific date for the illustration or indeed for the publication, but Great Bear was the largest loco around and the North British Locomotive Company was experimenting with an Electro-Turbo-Loco or steam turbine, which I gather was around 1910. (Having looked at an article in the book on Railways at War, the First World War had started, but doesn't seem to have come to an end, although no dates are mentioned. So I have revised the date to circa 1915.)
This a bit early for Paul Townsend's Highbridge layout, (see scalefour.org/forum/viewtopic.php?f=50&t=1867&sta... for details) but I thought he might like to see what would have been passing in an earlier era. I don't think the postal staff had to travel in those positions! This illustration had been uploaded after this photo had sparked a conversation on Flickr about the Highbridge mail apparatus This photo is now here at www.ipernity.com/doc/364457/26454919