This Mounted trooper may be a member of the Royal Artillery or possibly another mounted (cavalry) service.
According to Dress Regulations of 1900 Artillery and most other mounted units should had a gold lace band on the
Forage Cap. This man's cap has a dark band. This image needs a bit more looking into.

Cabinet Photograph
R. W. Elliott - Photographer
93 High Street, Aldershot, England
c. 1890's