Likley Dartford. Kent History Forum picked this up, and one of the clever people over there has added some info.
http://www.kenthistoryforum.co.uk/index.php?topic=11676.0
Interesting thought. I wonder why he isn't on the CWGC lists. He died in 1921, and presumably on service, so should just fit in. There's a Walter John Carvosso, of the King's Rifles, died September 1916, on the Thiepval memorial - presumably a relation.
From FreeBMD, the family appear to have originated in the West Country, before coming London way, with some in Lincolnshire.