Have to remember, the battle over Britain did not involve just fighter aircraft. I think the movie is generalizing a bit much, making it more romanticized by having fighter pilots crashing in neutral Ireland. The first Germans interned was a bomber crew, which is more plausible...
http://www.esatclear.ie/~curragh/klines.htm
As for Hess, he flew to Scotland on a peace mission, his aircraft being the twin engined Me110 and also had an extra large fuel tank installed for this very purpose.
regards,
Jack