I believe the French and British plan at the start of WW2 was to just wait out the Germans and hope the British blocade would ruin Germany's economy and lead to a regime collapse. Did the British have any plans for a gradual increase of the BEF from the 10 or so divisions on the ground that they had in May 1940? This could fit in with a ATL for a later German invasion combined with a bigger BEF, not sure if it will make much of a difference, maybe just a bigger, messier Dunkirk scenario.