I cannot see enough of the shoulder titles, so this could either be Royal Artillery or Royal Field Artillery.
Its definitely Royal Artillery. Its the identification of which branch its is. Sadly as mentioned the shoulder titles are not visible
It could be
Royal Field Artillery
Royal Garrison Artillery
Royal Horse Artillery.
There were separate badges for the RHA until much later after the war.
But his spurs and puttees we can tell he has a mounted role of some sort, but as the British Army was not fully mechanised until 1937, the world and his wife used horses, even the infantry.
The bandolier is not indicative or any branch or arm in any photo. There was indeed a mounted version of this item of kit, but...the indicators are x4 more pouches on the rear, so sadly its never a help.
The 1903 pattern bandolier equipment was for all arms and branches of the infantry, and indeed the belt and bandolier were still being made in ww2 even though they had been superseded by the 1908 and 1937 web equipments. The full kit included ammunition pouches on the belt and various other items included the mounted and dismounted bandoliers.
Prior to 1908 the Volunteer Artillery units wore silver badges...It MAY be that that he is a pre war Territorial who is wearing his old badge