On June 13 1940, Winston Churchill made the last of several flying visits to France. He did this at some personal risk: at one point his plane came within sight of a squadron of German fighters, but was not noticed. His aim was to try to persuade the French government to fight on against the invading Germans. But unbeknownst to him, the French had already decided to make a separate peace with Hitler, in direct violation of their mutual defence treaty with Britain.

The French Prime Minister Paul Renaud opened the meeting with a hypothetical question about the “solemn pledge that no separate peace would be entered into by either ally”: If France nevertheless made a separate peace, what would Britain's attitude be? It would, he said, “be a shock if Britain failed to concede that France was physically unable to carry on”.

Churchill said that under no circumstances would Britain reproach France for any such decision, but that this was different from releasing them from the obligation. And he spoke of practical plans for a rearguard action, giving time for the bulk of the French forces to withdraw to North Africa, so that they and the powerful French Navy could carry on the struggle from there. But whatever France decided,

At all events England would fight on. She had not and would not alter her resolve: no terms, no surrender. The alternatives for her were death or victory. That was his answer to M. Reynaud's question.

(From The Second World War by Winston S. Churchill. Book 3: The Fall of France.)

After some fruitless to-ing and fro-ing, Churchill gave up. But he had one last favour to ask of his erstwhile allies, a favour which was of desperate importance given the nature of the battle which their surrender was about to precipitate:

Before leaving I made one particular request to M. Reynaud. Over four hundred German pilots, the bulk of whom had been shot down by the RAF, were prisoners in France. Having regard to the situation, they should be handed over to our custody. M. Renaud willingly gave this promise, but soon he had no power to keep it. These German pilots all became available for the Battle of Britain, and we had to shoot them down a second time.

Let's hope that the same will not turn out to have happened in this case.