The notes for WW1 say they are for 7,703 British Army Officers who were Prisoners of War between 1914 and 1918. However, the first person I checked was a Canadian, G. W. Northwood, and his record is included. He`s listed as rank: Capatain, service: Infantry Canadians. The additional information available by pay per view or subscription is Section (meaning where serving); date missing; and Interned (which gives the country and what appears to be the date of repatriation).
For WW2 there are three sets of records:
Prisoners of War 1939-1945 – British Navy & Air Force Officers: 19,229 records
Prisoners of War 1939-1945 – Officers of Empire serving in British Army: 39,808 records
Prisoners of War 1939-1945 – British Army held in German territories: 107,000 records
The records will usually provide you with the following information about your ancestors: name, rank, regiment, army number, camp number, Prisoner of War number, camp type, camp location and extra notes, where applicable.
The first record I checked, for A.M. Reid in the British Navy & Air Force Officers series turned out to be a Canadian airman interned at Stalag 334 at Lamsdorf. However, the other I checked were British.
The source given is Naval and Military Press Ltd so you might want to use these are clues in looking for original records.
It`s worth checking this source for Canadian POWs despite the title.