80's children's sci fi, future in Britain, class segregation boy sent to special school for gifted

Hi,
I'm looking for a 1980's children's/teen sci fi book set in the UK in a very segregated class society. I seem to recall that it follows a boy who does too well in school and tests out of the middle classes so is forcibly transferred to a special school for gifted. Eventually I think he escapes and is either recaptured or something and maybe becomes a motorcycle racer? I may be completely wrong but I think there was a '5' in the title.
Thanks for the help!

I think this is Futuretrack 5by Robert Westall. At least the motorbike and the segregated class system fit.

Thank you, that's it. You made my day! Haven't read it since I was about 12 but it's stayed with me all this time. Going to try and find it at the library to reread as I think it's out of print now.