Sgt. Finigan's medal refers to 15th London Regiment Prince of Wales Own Civil Service Rifles. My grandfatther served in this regiment and his number was 4100.
I recommend you to read Jill Knight's wonderful book ' The Civil Service Rifles in the Great War - All Bloody Gentlemen.' This was a Territorial Army unit based in Somerset House in the Strand, London, and made up of Civil Servants, Post Office workers, bank clerks and men fron City offices. They were generally well educated and articulate and looked on the regiment almost like a gentleman's club. They suffered heavily on the Somme, and Paschaendale, particularly in the battle for High Wood.
Also, post a question on ' The Great War' forum. Remember to give as much information as possible and someone will come up with answers. An excellent WW! website.
Good luck.
Derek