Among the non-British pilots, at least 141 were Polish, 84 Czech and 28 Belgian, but only 13 were French and none were Dutch, Norwegian or Danish.
The reasons why there were many Polish, Czech and Commonwealth pilots are clear enough, as are the reasons for the relatively low number of Australian pilots.
The reasons for the lack of Norwegian and Danish pilots can also perhaps be explained: there weren’t many of them in the first place, and reaching England was probably more difficult for them than the French, Belgian, Polish and Czech pilots who fled at the fall of France.
France, however, had Europe’s largest allied air force at the time of the Battle of France (764 fighters), which presumably means they also had far more pilots, yet only 13 or 14 French pilots fought in the Battle of Britain, compared to 28 pilots from Belgium (81 fighters). And what happened to the Dutch (up to 76 fighters)? Of course, some were killed in action before the Battle of Britain, but that was also true for the Poles (about 280 fighters in Set. 1939) and Czechs.
I’m wondering if the formation of Free French Forces destined for North Africa had anything to do with the lack of French fighter pilots in the Battle of Britain. However, given that the RAF had more planes than pilots, that surviving French pilots had invaluable combat experience (as did the Poles and Czechs), and that the fall of Britain would have been catastrophic for the allies, surely the Battle of Britain had to take priority over anything else?
Note: All the figures cited for fighter planes refer to operational planes. It seems fair to assume that the number of operational fighters was not hugely different from the number of available pilots.