Wasn't he from New Zealand?
Thats the Red Runs the Vistula fella you are thinking about,and he was a Brit who after the war moved to New Zealand.
Quite a few non Poles found themselves working for or actualy members of Polish underground groups. Many were escaped POWs from the camps built in Poland/old Germany.
If I remember rightly during the Uprising Slovakians made up the largest national group.