How many units did Britain from former Polish forces or Belgium or Dutch? And who had command over these?
Specifically with Poland there were a few famous units that were formed by different allied powers later in the war. The 303 Squadron was a Polish fighter squadron who flew in the Battle of Britain with many aerial victories and numerous fighter aces during the battle. The Polish 1st Corps fought with the Canadian 1st army in Normandy (Falaise Pocket) and across Northern Europe towards the end of the war. The Polish 2nd Corps fought in Italy nearly the whole war and notably at Monte Cassino. And all of these Polish soldiers were under overall British Command and were given mostly English supplies and equipment also. There was a small Polish army who fought under Soviet command on the Eastern front but I am not as familiar with them or their exploits.