One factor overlooked was the Bf 109E had barely enough range to spend 10 minutes over London... dogfighting over Ireland... Not possible.
That's the biggest 'oops' I've seen folks comment on. Not much chance of a 109E fighting a Spit V over Ireland. I did the 'suspend my disbelief' bit as it initially reminded me of an old Roald Dahl story about an RAF and LW pilot who get locked into that kind of fight to the death even after they are on the ground. Had it been a Ju-88 or He-111, it would not have really allowed that 1 v 1. And that I think was the key to keeping the focus off the 'surprise' at the end.
Interesting that this showed up not too long after that Spitfire excavation in Ireland of a bird flown by an American in the RAF, who was briefly interned there.