Wow. Kudos to Mr. Jake Gyllenhaal
Very, very few American actors can manage a consistent 'English' accent. (Received Pronunciation) And I include Peter Dinklage of 'Game of Thrones', whose accent ranges far and wide, even within the same episode. My ears bleed when I hear an American -or Canadian- doing an English accent badly. (Yes, I'm a snob.)
But Jake does a superb job in this film with his accent. I was consistently shocked at how well he executes it, even in scenes where he's under a lot of pressure.
Well done, you.