From where did you find Doncaster?
FreeBMD is showing a Reginald Herbert Bettany, registered March qtr 1909, Poplar, Midlesex.
and Reginald Bettany, registered December qtr 1911, Cheadle, Staffordshire?
EDIT:
Must be the Poplar one?
There is a marriage in 1938 (also) for Reginald Bettany in Cheadle.