Picked this up today local to me. The officer in the middle appears to be a Lt. Colonel in the Royal Army Medical Corps and is apparently missing his left hand. The two sergeants with canes are both probably wounded and have an unusual twisted band on their caps. The one on the officers right is I think from the Welsh, though it could be any of the units that wore the Prince of Wales's feathers, such as the Pembrokeshire Yeomanry or the 3rd (Prince of Wales's) Dragoon Guards. The other is wearing a Light infantry or rifle regiment bugle badge, and could be King's Shroipshire Light Infantry, 6th battalion (Rifle) King's Liverpool regiment, Durham Light Infantry, Oxford & Buckinghamshire Light Infantry or the Nottinghamshire Yeomanry (Sherwood Rangers).