Good evening,
Definately a cavalry man, he is wearing a 1908 cavalry pattern sabre. The greatest cavalry sword ever made but b******* heavy when you have to carry it in hand on parade for an hr or two.
He could be 1st or 2nd Life guards, Horse guards, 5th dragoon guards or 7th hussars. They all wore that shape of badge but without being able to see the detail in the centre it is impossible to tell.
John915
Added, if he managed to enlist in his local cavalry regt then 7th hussars.