The cap and shape of the cuffs indicate c1904 to WW1. He has a good conduct 'badge' above his left cuff for two years good conduct. A second was issued after a further five years. So at least 2 to 7 years service as a Regular soldier.
Depending upon his date of birth then his service record may be in the group for WW1 which were two-thirds destroyed during the 1940 blitz. Men enlisted for 12 years after the age of 18. So if his 30th birthday was after 1st January 1914 then he would be classed as 'WW1'. The last five years could have been in the Army Reserve so he may be in the 1911 census as a civilian, but still in the army.
The dark cuffs are probably blue indicating 'Royal Regiment'. I dont recognise the cap badge as being one of the Irish ones. A better scan of just the cap badge would help. It could be topped by Prince of Wales feathers. It is not one of the fusilier regiments.
Can you give more information about his age, his wife, date of marriage and when the children were born (if known).
Ken
