Those of us old enough to have lived through that period have it burned into our memory, a 40 something born half a century after, is not going to perfect in the minutia of the period, not that is unless they were history graduates, and possibly not e ven then if they were, speaking off topic so to speak. I can get a little peeved ,when those with little better to do than criticize pick up on such spurious detail- after all -as a 40 something my self- nearly 40 years ago I could not put my finger in the precise detail of who was with who in 1914. Anyway by 1940 - was not lend lease well under way? Perhaps we were not entirely alone - even if the U.S.'s entry was nearly 2 years hence.
It has to be said that after Dunkirk the UK was in full retreat. It is highly unlikely that we would have been able to push forward had it not been for a huge amount of help. Junior partners, maybe not but we were in a dark, dark, solitary place as anyone can read from Churchill's' excellent memoirs.
'Have you forgotten the Battle of Briton??.'...you need to revise your history very carefully and rather strangely, Churchill was of the same opinion as myself...or should that be the other way round. We were in full retreat and very much on our own in the proverbial barbed wire canoe.