Ha! Ha! So you can call yourself half-white as you have lived almost half your life in the UK!
Just over a decade back, a private hospital in a ME country had hired several very professional doctors from the US. When they arrived. it so happened couple of them were black Americans. The Arab employers reduced their offer as the blacks were not considered to be "real" Americans! The entire group (both blacks & whites) resigned immediately and went back. As such, you may also get measured by the same yardstick even though you hold a British passport.