This man is mis-filed as MARLER in the WW1 Service Records (WO 363):

William David MAILER joined the Queens (W Surrey) Regiment in Mar 1916, declared age 40y 6m. He was a Drapery Salesman, living in Tottenham, London.
Mother ANNIE lived in Blairgowrie, Perthshire - which is where he went on discharge in 1919.

Birthplace not stated - Scotland? or possibly Q3 1875, Hayfield?
Served as Pte 8639 (Queens), 86705 (Labour) & 80305 (RDC).

Anc****y, MAR, pages 70978-70993