I may be wrong (it has been known to happen!), but I think the WW1 Service Record for Clemmens SCOTT is really for a man surnamed CLEMMENS, and so is mis-filed (WO 363). Could he be ERNEST WILLIAM SCOTT CLEMMENS? Hopefully the details will ring a bell with someone searching:

Enlisted (Dragoons, Reg No 8024) August 1914, London, declared age 20yr, born Smithfield. Father ERNEST ROBERT CLEMMENS. Home address Chancery Lane. De-mobbed 1919, Reg No 13363

Anc****y, SCO, pages 86955 to 86958