No it's not. That's a term which has no legal, historical or geographical basis.
, among others, would disagree at there being no "historical or geographic basis". It's certainly, though, a term that's fallen out of use subsequent to the assocation of "Britain" exclusively with the UK and the independence of the Republic of Ireland. Not wholly different from Canadians and Mexicans being "American" in the sense of the American continent, in that it's technically true but has issues due to the association with the USA (usually somebody would say "North American").
Some big news, on an actual movie-related front.
Counting Cap and Bucky, that's four members left; Union Jack's a given (John or Brian, I wonder?), he's of a similar powerset and makes an obvious counterpoint to Cap himself. Don't know about the rest (they're described as being representatives of European countries, which the Invaders never really were in the comics; foreign membership was primarily two Brits and an Atlantean; maybe they're planning to make up a few new characters to represent France, Poland, or wherever?).
I'll be interested to see if they're planning to bring in other characters with genuine super-powers. I mean, if the Brits have a chick who can run at the speed of sound, how impressive does that really make Steve look? Conversely, having such obviously superhuman people might give Steve a chance to demonstrate just how important he is, even if he's not the most physically powerful