What is Americans doing......

....flying helicopters in London over Parliament and allowing US troops to come into contact with British subjects fully armed? (Which I may add, would be highly illegal, and result in them being arrested - and the chopper would probably be shot down that close to Westminster).

This is completely wrong. Americans can't come into British airspace (they've tried that before and nearly got shot down - were it not for British restraint).

I know that this is only a movie, but this is like British troops arriving on the Whitehouse lawn uninvited to save the US President, without an American secret service agent in sight. Yes, my friends, completely unrealistic.