could be a BSA M20, but need good eyes! maybe a Royal Enfield? What country is that soldier from? The ATS (Auxiliary Territorial Service), the women's branch of the British Army in World War II. Ariel W/NG hmmm, the Ariel W/NG has a ohv engine and the bike in the pic seems to have a side valve engine, I see a lot of space between the cylinder head and the fuel tank. The Triumph HW and Matchless G3/L also have ohv engines. The toolbox also does not resemble those of the most common sv bikes: BSA M20 and Norton 16H. A Royal Enfield is the only sv bike with a similar toolbox, so I think it's a Royal Enfield WD/C 350
I had an ex WD 350 side valve Royal Enfield about 1955 Reg No OMK 419. I was working on a warship at the time and was able to take it ashore in Gibraltar and ride it to Malaga and back. The modern holiday resorts of Fuengirola and Estapona were tiny fishing villages then.