You may be able to find casualty lists of British Soldiers who fell during the Battle of the Somme. I have some thoughts which may or may not be helpful. First, you might see if The Imperial War Museum has a web site. Given the depth of information they have on, say, Waterloo, they may have a similar depth and richness of information in The Somme.
Second, examine the uniform closely and see if you can tell exactly which markings it might carry. Some of the people at the Imperial War museum may be able to help you track down Regiment by some of the markings on the uniform, or even by details on the tie, if it is visible. These are sometimes distinctive.
Third, do not go in with the assumption that that your Captain must be English. There were a lot of Commonwealth soldiers involved, and your Captain may have come from New Zealand or even Ireland, which sent an enormous number of troops to fight for Great Britain during World War I; many more, I believe, that rose against it during the Easter 1916 rebellion. Given the difficulty of the name, the possibility of a South African Captain might be taken into account.
If The Imperial War Museum doesn't have casualty lists, and can't help you identify regiment, I'm uncertain where to go, but they might be able to help steer you toward other sources. Some of the Regiments were "Pals" Regiments, where the ranks were filled out by groups of friends from similar social or occupational groups from a single geographic area. Most of those, I believe, came later in the war, but I'm really not all that sure of myself here. I believe that the officers were moved from regular army ranks, however.
I hope some of these odd directions might prove helpful for research directions.
Sincerely, Bob Kaven