>Brits are Romans
No. You must be Sam Cooke, because you don’t know much about history.
The Roman population in Britain was limited to a small administrative elite and legionnaires from around the Empire. Relatively few remained after the waves of withdrawal for defense of the collapsing Empire.
Britons are Celts - predating the Roman invasion and predominantly in the northern and western fringes - and the rest of us are Angles, Saxons, and other assorted Germanic and Norse tribes. We got another Norse infusion after 1066. There were small influxes of: Flemings in the Middle Ages; Huguenots after the Reformation; and some Jews and Dutch after the Glorious Revolution. And that was largely it, until the 1960s.