On Freemasonry practiced by prisoners-of-war.
"Little is known, however, of the activities of English brethren in French hands. Thorp tells us that there is only one instance on record of a lodge being held amongst them during their detention (No. 183, "Antients"). It is a fact, however, that many individual brethren on parole attended French lodges as guests. Again, it is known that some were relieved and assisted by their French brethren, who also made representations to the authorities to make the lot of the English brethren less harsh. It is believed that the escape of some was also made possible with French help and connivance. Indeed, a pamphlet was published in Paris in 1913 accusing French Masons of so doing. A translation of the pamphlet appeared in the Leicester Transactions, 1923- 24."
"Vibert records a lodge of British soldiers imprisoned in Kongsberg, Norway, in 1807."
Thorp, J. T., French Prisoners' Lodges, 2nd ed., Leicester, 1935 ; 304 pp., illus. Further discoveries since 1935 are recorded in Trans., Lo. of Research, Leicester, by S. Kay, 1950-52, pp. 33-44, and 1959-60, pp. 18-29; J. Bossu, 1957-58, pp. 62-74, and 1958-59, pp. 39-54.
Vibert, Lionel, "Masonry Among Prisoners-of-War", in Sussex Masters' Lodge Trans., 1937, pp. 4-26.
There is also a book but not certain how much on British prisoners:
"Behind The Wire" By: Keith Flynn OBE. An intriguing account of Masonic activity by prisoners of war, from Napoleonic times to World War II. It is published by the Freemasons.
I think that there is a full report on prisoners-of-war in the Parliamentary Papers furnished by the Admiralty in 1814? Now it is probably more on the French prisoners held, but, there may be references to British prisoners held. Countries at the time were responsible to pay for the upkeep of their prisoners in enemy hands.
See also, http://www.sw19j.com/British_1.html. It has information on a few letters sent home by British prisoners.
I thought there was some correspondence on the subject of exchanges and parole in the despatches but cannot recall the year. There was an exchange rate set up as well. See 2nd Duke of Wellington, Supplementary Despatches, Correspondence and Memoranda of Field Marshal Arthur Duke of Wellington Volume 6. London; 1860. See also Statistical Abstract of the Napoleonic Wars: Great Britain's Army on this forum.
Hope this helps.