So, I'm 100% sure that I am male to female transgender, However, I also have a powerful desire to be a different race as well (I'm white British). What does this mean?

Your ethnicity is something that you cannot change, just like you can't change your gender identity. While you can undergo transition to match your body with the gender you identify as, there's not much you can do about ethnicity. However, you can always offer solidarity to ethnicities that are misjudged or disciminated, and help build a more inclusive environment fof them.