Great find, the No. 1 set . I know of a guy in NZ with one . He told me it performs very nicely . The markings on your example , looks like a Canadian arrow ?
The signals units here used them too, a very small number of them were issued before the war . A pre war militia veteran in Adelaide, Colin Wagner, used the No. set , I believe he is still alive . Andrew Tostevin in Adelaide has compiled some info . His scan of the manual is here
http://tosty.id.au/BRIT-1-MANUAL-AU/