The First Class Honours degree, in my (albeit limited experience) is considered equivalent to a Summa cum Laude, so I don't see why they would downgrade that. As for the GRE scores, with history programmes they are honestly reviewed with a big grain of salt. Generally-speaking, if one's score is abnormally higher or lower than the average, they might take a second look, but overall they don't factor much in the admissions process. It is much more important to have outstanding grades, LORs, and accomplishments.
That's at least what my POIs have discussed with me.
Which British institution did you complete your BA at (if I might ask)?