Can you provide any additional details? The British army was a very different creature in 1918 than it was in 1916 or 1914. Infantry, cavalry or artillery? Western Front, Italy, East Africa, Balkans, Gallipoli, Mespot, Palestine? Grizzled trench veterans or fresh faced idealists? Regular army, Territorials, Pals?
My personal recommendation is for the Royal Welch Fusiliers. Find your pal a copy of 'Goodbye to all that' by Robert Graves, should give him all the background he needs (and more, especially of the true horror of the Western Front, all that bloody poetry!)