Real photo postcards from World War One.
He is a member of the Signal Service of the Royal Engineers Chris, as identified by the large RE shoulder title and the double signals arm bands. This Service grew exponentially in importance during the war, with the first wireless sets in use during 1918. After WW1 they broke away and formed their own discrete Corps, the Royal Corps of Signals.
The funny thing is that in my inventory I have him marked as a Royal Engineer. I don't know where I got The King's Liverpool from when I posted this. Thanks for the correction.