John.
I don`t mean to poke my nose in, just trying to help, but if you click on the link that Pollypops has provided, and when that page opens click on the red box that says "see casualty records", this will bring up a list on which you will find George.
If you click on his name in the list, a page will open up offering you the option to "view certificate". It is this to which Pollypops was referring.
I`m afraid that you won`t find a cause of death there, but if he was listed with the C.W.G.C. then his death would have been WW1 related. Further, if he died in 1919 and is buried in this country, the most likely cause would have been "Died of wounds". Anyone killed over there was buried over there.
Hope this has helped, but further research on your man will be necessary to find out all the facts. Good luck.