The badge Willie is wearing is the Imperial Service Badge. A lot of the guys photographed in 1914 and 15 are pictured wearing this badge. I generally have a few of these lying about; now pictured below. The copper one below is I believe a worn silver plated version.
The territorial soldiers who joined pre war were actually not obliged to serve overseas, they joined for home service only. Service overseas was voluntary, and when war came volunteers were called for for overseas or 'imperial service', these volunteers signed an agreement and were give this badge to show they had done so.
It's a great shame these badges were not individually numbered; would have been an interesting collecting field! I actually found one of these on the Braid, along the tip edge at the high water mark.
