M.W.T. Co. Ltd is Marconi in the UK. I suspect this is one of the sets that was obtained by Canada for training. Inside you'll probably find valves, not tubes.
RCCS was in a sorry state prior to the war due to austerity. In the 1920s & 1930s they were still using WW1 equipment as well as commercial sets.
The first set actually made for the army was the WS1 made by Northern Electric Co. Ltd. They made 100 sets. That would be a nice set to find.
Nice score on the WS29. That's one that is on the rarity list.