John BALFOUR, a Prisoner of War wrote "Ruhleben Poems" published in "Estonian Review, 1919.
Archibald Allan BOWMAN (a POW in Germany) published "Sonnets from a Prison Camp" in 1919 with the Bodley Head publishing company.
Frederick William HARVEY (DCM, Lieutenant in the Gloucestershire Regiment). Prisoner in Gutersloh and Crefeld. "Ducks and other verses", published by Sidgwick and Jackson, 1919 and "Farewell", Sigfwick & Jackson, 1921.
R.H. SAUTER, "Songs in Captivity", Heinemann, 1922
Lieutenant John STILL with the East Yorkshire Regiment (POW in Turkey), "Poems in Captivity", Bodley Head, 1919
Alec WAUGH (brother of Evelyn), Dorset Regiment, taken prisoner in 1918. "Resentment", Grant Richards, 1918.
I am sure there must be others and will do my best to find them.