There are those "experts" who cannot be bothered to learn the Jewish perspective about anything. The ideas "Lost Tribe" is expressing are from the 19th century movement called "British Israelism" -- basically, the belief that the Celtic and Anglo-Saxon peoples are the Lost Tribes of Israel. Evidently, they believed that God is a practical joker -- why else would He have all these Jews go to the Synagogue, study Hebrew, etc. for thousands of years while all along the "real" Israelites were revelling in their Aryan purity in Scotland, England, Germany, etc.
The modern offshoot of British Israelism is the so-called Christian Identity movement, by the way. While the followers British Israelism were content to believe that the British Empire was the Kingdom of God on earth, the members of the Christian Identity movememt seem to have a fetish for the Third Reich. Their idea of heaven seems more like hell to me. Do a search for "Christian Identity" and you will quickly find some very unsavory things.
Those Klu Klux Klansmen are real nut jobs, they forget that if they are Christians, they are following Christ who was a Jew from the Middle east -- a brown skinned man. Christianity is not about the color of a person's skin or how they look like. KKK are disgusting, and when they try to potray themselves as conservatives, that's een more disgusting -- they give us, true conservatives, a bad name and they drive the blacks (most of whom in the south are conservative, God-fearing, pro-family, pro-life folk) away to the seedy democrats