OH is convinced about GSC being around in WW!, now I have this link too:
http://www.militaryheadgear.com/items/9137
but he also says that, as the photo is not too clear, it could also be Manchester. That's what I call hedging your bets

Dont trust everything you read on the internerd....

First of all, that is an officers General List badge, used for officers not attached to a unit...One can even find RAMC doctors with that badge
Second, the hat features an ORs chinstrap, not an officers one
The Manchesters had the coat of arms of Manchester as their badge...Part of which in seen in the club badges of United and City.
Because of the bit sticking out of the top, and no scroll...it is patently not Manchesters....
It is the Royal Coat of Arms of the Volunteers, and as it is not the "Labour Corps", there are no rifle and pick collars, nor is the shoulder title Labour or Pioneer