This man joined the Kings Own Scottish Borderers (in 1895) as Thomas CLARKSON, but in 1890 signed a declaration that his true name was WARBURTON. Consequently his papers are "mis-filed" in WO 363 (WW1 Service Records):

Thomas WARBURTON, mother ANN, home address MILES PLATTING, Manchester.
Joined the KOSB on 3 January 1895, stating age 22y 4m, born HULME.
Regt No: 5130 (Private); S Africa 1899-1902
Served his standard 12 years until January 1907.

Anc****y, CLA, pages 193150-193155