1899 Nov 24. Born St Pancras, London
1901 census at 18, Piercefield Street, St Pancras, London
1911 living at Hampstead
1918 Died in France ??
1920 Nov 12 enlisted with RIC no 75440 . Engineer
1922 Jan 26 |Disbanded from RIC
He is never heard of again
I can only conclude that someone has used his name as an alais to join the RIC. The most likely person was probably a younger brother Robert Percy Hagg who was only 16 in 1920 and lived for may years after the end of the war. With no further information, it is impossible to prove what has happened here