The essence of British Israelism is Replacement Theology which in practice is anti-semetic. While descendants of lost tribes may be in America and elsewhere (in many instances only G-d knows who they are), G-d has an everlasting covenant with the Jews and didn't cut them off nor will he replace them. Too many Christians apply "everlasting" to their own promises, while failing to meet the conditions, and at the same time deny "everlasting" applies to Israel.
How so? Queen Elizabeth can trace her ancestry back to King David, did you know that? Maybe you shouldn't be so keen on reading words of men about the USA being Mystery Babylon, which is so stupid in and of itself, (do you even know who founded Babylon and what it means?) and pay more attention to what the Bible actually says. For instance, how does the prophecy of Ephraim (a host of nations) and Manasseh (a great nation) apply to Israel (Judah) today? Or any of them, for that matter? There isn't too many nations around today that obviously fit the Abrahamic Covenant, so that should make your job a little easier.
I you want to read the words of men, I'd recommend EW Bullinger and Raymond Capt over some cheese puff who thinks the USA is Babylon.
Would you please quote the Bible verse(s) which establish an EXCLUSIVE everlasting covenant with the Jews?