You might not even have to rule Oxford out.
If the high school you went to was poor then they will still look favourably upon your results. Of course, idk your exact situation and, I mean no offense (this applies to me and over 99% of the world as well), the likelyhood of you being Oxford material is small.
Only 8 GCSEs? Or are you omitting those which you got less than a C in? I did 13 (though I'm always told that's a lot) so 8 seems like really few.
That said, provided your A* and As are in the relevant subjects I don't see this being a barrier to going to top Russel group universities. You'll still get predicted grades which are supposed to effectively indicate what you'll get at A2.