There is something about this pic....
Certainly WW1 period, as ainslie has pointed out...The chinstrap on his hat is also a pointer....it is narrow.
There are nil collar dogs, his Sam Browne looks like it has been "acquired" from a taller chap...The cross strap has been worn some 4 notches further down, and for some time. there is also something rather odd about his epaulettes.
"Wind up" jackets with rank on the shoulder were not unknown as early as 1915. Also the Guards did not wear cuff ranks at all...they always wore them on the shoulder.
His puttees, worn in a dismounted fashion look rather like other ranks rather than officers...
Nearly everybody in a position of repute in WW1 wore a uniform which would pass as an army one, from the Red Cross to even the Boys Brigade!!
I cannot make out the cap badge and if possible and as requested, a high def scan would help.
He may appear on the Army Lists of WW1, and he can be traced thus, also via the London Gazette: this is searchable on line. The Army Lists can be found in libraries and a number of Regt museums. If he appears on neither, he may well be one of the WW1 "paramilitaries"
