Upvote:1
Your Grandfather in the first photo is wearing the khaki service dress for officers of the army which included a lapel-led tunic introduced in 1908 with a shirt and tie which became khaki like the tunic from amendments of the 1st of August 1913 he also wears the standard Sam Browne belt issued to all officers from 1900 onwards. The second photo of him shows him to wear the 1902 pattern service dress introduced to lower ranks (not officers).
Uniform for Officers updated by the 1913 Amendments. 1902 Pattern service dress