I am afraid I cannot answer your question as I have not come across this subject before. However, you maybe interested to learn that there is an excellent book titled The Broken Column. It is a true story of an English submariner whose submarine was sunk. He was captured then escaped. Instead of escaping he went and fought with the Italian partisans! A good read!,
I think there were roughly 70,000 Commonwealth POWs, but I am still unclear how many escaped to the Partisans. They certainly numbered in the thousands, as an escape organization hidden in the Vatican City State had a card index with at least 2,000 names.