I would love to see proof as well, because I'd like to know where they were from in France/Brittany.
My father and Fouche relatives all say that they are descended from French Huguenots. Whether that is from the Bible record or has been passed on directly from the first generation and on down is anyone's guess. My great uncle still lives quite close to the orginal property in Loudoun County, so there hasn't been much physical movement at least to disrupt the family history.
Also, many of the Huguenots escaped to England and sailed for America from there, so it's no guarantee that an ancestor was British. I have a Swiss ancestor who sailed from England. I've also found a concentration of Fouches around Nantes, which was at one time part of Brittany. That's not evidence, but it does give weight to the story.
If you do come across any documents, please let me know.