The difference was that in 1940 the only internationally recognised French government was at Vichy and not at war with Germany (actually allied with it), so any Frenchman wishing to fight alongside Britain was legally speaking a traitor of his state/government.

This is where my confusion lies as I was sure that ‘Free French’ forces were operating, and were recognised (by Britain, if not by the United States), much earlier, while the Vichy government was still very much in power in France. I know for example that the French submarine Surcouf was boarded in Plymouth harbour (in an infamous incident) by Royal Marines on 3rd July 1940 (at the same time as Royal Navy battleships were shelling a fleet loyal to the Vichy government at Mers-el-Kébir) and was operating under the Free French flag shortly afterwards. Later in July 1941 when Surcouf was refitted in the United States the refit (costing $800,000) was paid for under the Anglo-American Lend-Lease programme.

I did not know that there was no actual surrender of Polish forces in 1939 (confusing this with the surrender of Warsaw)!