Turnell is a fairly rare name. The only candidate at Brentford arouund theat time was William Harpur Turnell who was born 8 Oct 1888. That man appears to emigrate before WW1. So this man appears from nowhere and disappears to nowhere
1889 Feb 10. Born Middlesex (same date RIC and Army)
1891 census at Brentford
1907 May 13 Enlists in 1st Dragoon Gds, He is a Blacksmith
1911 census in 1st Kings Dragoon Gds
1919 Dec 16 Discharged to Z Reserve
1920 Feb 7 Enlists in Royal Fusiliers. He is a Shoeing Smith and had served 0ve 12 years in 1st Dragoon Gds and 1st Reserve Regt of Cavalry
1920 Oct 11 Discharged
1920 Dec 28. Joined with RIC no 77101 & ADRIC no (482). ex-Army
1921 Jan 28 Posted no 2 Vets from Gormanston
1936 There is a Harry Turnell who is a PC at Fulham in a newspaper article. But I cannot fing anything more on him and no death cert.