Invasion of Romans and 500 years latter Normans, Norse, from Northern France did not change British genetics much but brought a bit of civilisation.
Er,yes,thanks for that Roman "culture" hmm, Slavery, Gladiators,religious persecution,no rights to women,children,non citizins.Of course,so much more cultured than the Celts wernt they,after all,the celts were barbarians who had sexual equality,rights to fair trial, laws protecting the elderly and children,while in Rome,unwanted babies could legally be left on the city rubbish dump,some civilisation....
And the Normans were the same stock as the earlier Viking invaders of all parts of britain,bythe time of the conquest "english" and " Norman" culture was practicaly the same. PS the Saxons were around a long time after the arrivall of the Normans aswell,all becoming "english" at a later date.
anyhoo, If you can trace your ancestors back in the UK anything over a hundred odd years you are more than likely european(with some indo european in the mix now and then) Being the simple fact,that everyone seems so scared of these daysthat ALL white peoples origionated in europe( lord yes,before someone says the obvious,we may well all have started in africa,but that is still only hypothetical,,)