He surfaces as a 2nd Lt in 1913, which at that time implies a certain class level. He resigns his commission in WW2 to enlist in the ranks.
1888 Mar 27.Born Ripon, Yorkshire. Certainly a Birth Register entry also for William Cockfield in Oct/Dec as well.
1891 census. Living at 16 King St, Ripon. Ancestry give this as a possible name for William Cockfield but does not explain. There is a Thomas and Sarah Ann Gill living next door, and 2 Ancestry Trees ascribe him to that family. Apart from that I cannot get a reason. A Sarah Ann Gill married George Cockfield in 1886 in York
However there is also at North St , Ripon. I think this is more likely
1901 Census. In Ripon
1911 census at Newcastle upon Tyne, a Commercial Traveller
1912 Married Gladys M Reay at Morpeth
1913 Jun 14. 6th Battalion, The Durham Light Infantry; William Percival Gill to be Second Lieutenant. (To be supernumerary). This is a Territorial commission
1913 Aug 6. 6th Battalion, The Durham Light Infantry; Supernumerary Second Lieutenant William P. Gill is absorbed into the establishment.
1914 Nov 13. 6th Battalion, The Durham Light Infantry. Second Lieutenant William P. Gill to be Lieutenant (temporary).
1915 Jun 15. The Durham Light Infantry. Second Lieutenant (temporary Lieutenant) William P. Gill to be temporary Captain.
1915 Jun 20. Second Lieutenant (temporary Captain) William P. Gill reverts to the temporary rank of Lieutenant. Dated 20th June, 1915.
1915 Aug 28. 2nd Lt. (temp. Capt.) W. P. Gill to be Lt. (temp. Capt.).
1916 Jan 11. MC Gazetted. Second Lieutenant (temporary Lieutenant) William Percival Gill, Durham Light Infantry (Territorial Force
1916 Sep 22. Durham LI.—Lt. W. P. Gill, M.C., is seconded for duty with a Garr. Bn.
1917 Aug 15. Garrison Battalions R Munster Fusiliers. Lt. and Adjt. W. P. Gill, M.C. (Durh. L.I., T.F.), from Durh. L.I., to be Lt. (retaining present seniority), and to be Adjt. W. P. Gill, M.C. (Durh. L.I.), to be actg. Capt., with pay and allces. of Lt. while holding the appt. of Adjt.
1917 Aug 10. Lt. W. P. Gill, M.C., to be Capt., with precedence as from 1st June 1916, and to remain seconded.
1919 Jan 24. Capt. W. P. Gill, M.C. (Durh. L.I.), to be Adjt., 51st Grad. Bn., Yorks. L.I.
1919 Mar 1. Capt. W. P. Gill, M.C. (6th Bn., Durh. L.T., T.F.), ceases to hold the appt. of Adjt., 51st Grad. Bn., Yorks. L.I. 1 Mar. 1919.
1919 Apr 11. Special Appointment. Cl. FF.— Capt. W. P. Gill, M.C., 6th Durh. L.I., T.F.11th Apr. 1919
1920 Jan 25. 6th Bn., Durham L.I.— Capt. W. P. Gill,
M.C., is restored to the estbt.
1920 Sep 17 Joined ADRIC with service no 581. Posted to I Coy. Section Leader. His wife was at Ashville, Ripon,Yorks (same on MIC)
1920 Oct 21. Promoted Platoon Commander - DI3.
1920 Nov 22 Promoted 2nd in Command I Coy
1920 Dec 17 to 31 Dec on Leave
1921 Feb 28 Posted to J Coy. Company Commander . He replaces Seafield Grant who had been killed in ambush a few days earlier
1921 Mar 6. In command of a patrol that shot C Foley
1921 Apr 22 to 13 May in Hospital
1921 May 13 to 10 Jun on Medical Leave
1921 May 28. Reverts to T/Cadet - this is presumably because of his health
1921 Jun 13. Discharged medically unfit - not due to service in ADRIC
1921 Dec 22. Gazetted out of the army. 6th Bn., Durham, L.I.— Capt. W. P. Gill, M,C.
1939 Living in Ashford , Isle of Wight R.D., Isle of Wight, with Gladys Gill. He is a retired Major (100% disabled)
1940 Jun 18. Capt: W. P. Gill, M.C. (110611), late Durham L.I. (T.F.), relinquishes his rank on enlistment into the ranks,
1944 Jan/Mar Died Isle of Wight aged 55. He was not serving in the army as he is not on CWGC