what you got there, mick, appears to be a Brit version of what we call a "dollar watch." Probably circa late 1920s. No jewels, likely a pin pallet escapement, and in this case, pin set- that is you push the little pin on the top of the case while turning the crown to set the time. A cheap watch made to run for a couple of years and be discarded. The Ingersoll Yankee was the famous one here in the states, millions of them sold. Yours seems similar to that pattern, there were a lot of spin offs from the Yankee, some made under license in UK.
However, it is atypical for dollar watches to be pin set - all the ones I've seen are crown set. Roskopf movements - the more durable and well made European ancestor of the American dollar watches - were pin set. It's hard to judge from your photos if your's has some Roskopf features.
At any rate, a nice, collectible in decent shape but likely of little value beyond innate interest. It's typical of low end watches to have fanciful markings on the dial to enhance their value in a buyers eyes - thus "Services Army."
I'd guess this is a Swiss made cheapie for export to the British market, circa 1924.