Although I have not seen a lot of British films
and TV series, I am a big fan of "Yes (Prime) Minister" and "I, Claudius" . In those films I have
seen, Americans are frequently presented as uncultured
hicks, Jews are presented as hypocrites, Africans
as cannibals, the French as arrogant and shifty, the Germans as robotic militarists, the Irish as drunken troublemakers, etc. The Brits are
no strangers to stereotyping.
Two British versions of Americans came to my mind. One is certainly a nasty portrayal, and the other, while characteristically brave, is still a stereotype.
The "brave" American is in an episode of "Doctor Who" titled, "The Claws Of Axos". A Brit actor portrays an American CIA agent. The accent is hysterical and the character is over-the-top "gung-ho".
The nasty portrayal is in an episode of "Fawlty Towers". The American in "Waldorf Salad" is just one great big crabby jerk. However, it's a wonderfully funny character. But again, the accent is awful. Almost as bad as Michael Palin's and Eric Idle's horrible American accented Vacationing characters in "Meaning Of Life". Not to mention John Cleese's horrible American accented waiter in the "Would you like to have a conversation?" section of the movie. Again, a very, VERY Funny scene!
I certainly acknowledge that many "British" characters in American productions are not based in any way on "reality". I myself feel that I make up for enjoying those productions by absolutely adoring programs such as "Doctor Who", "As Time Goes By", "Mr. Bean", "Fawlty Towers", "Brittas Empire", "Black Adder #1 - #4", "Red Dwarf", "Campion", "Are You Being Served", "To The Manor Born", "Monty Python" and many, many, many other Top Quality British shows and movies.