I have a question about the British people and Britain?

There probably is no such thing a white 'Brits' as such. Our history is all about us being a 'mongrel nation' made up of settlers and invaders, immigrants and visitors from around the globe. I have no idea where you got the neolithic people description from...so I will not comment on it. The simple fact is that European 'whites' have been very good at absorbing other races both by building world wide empires (the British Empire was the biggest) and by interracial relations. There have always been Black, Brown, Tanned and Ginger Brits... and personally I hope there always will be...that is what makes us truly great.