This man served as Frederick William CLARKE and so is "mis-filed" in the WW1 Service Records (WO 363):

Harry Thomas McGREGOR joined the Berkshires (Regt No 8367) in February 1909, declared age 19y 2m, and left to join the "Regular Army" in June 1910. He served with the East Surreys (No 10019) and was killed in February 1915 (near Ypres).

Born in Willesden. Mother: Mrs S E HUNT (Formerly McGREGOR), of 75 Tapperfield Road, Nunhead Lane, Peckham.

Anc****y, CLA, pages 127072 to 127087