http://en.wikipedia.org/wiki/Star_of_the_Guardians
Star of the Guardians is a series of fantasy novels by Margaret Weis. The series consists of four volumes:
The Lost King, King's Test, King's Sacrifice, Ghost Legion
or perhaps you are thinking of
The Guardians is a novel written by John Christopher, originally published in 1970.
Set in the year 2052, the novel depicts a future, authoritarian England divided into two distinct societies: the modern, overpopulated "Conurbs" and the aristocratic, rarefied "County"; the former consists of crowded city districts and all-pervasive technology while the latter is made up of manors and rolling countrysides typical of 19th-century England. The novel follows a young Conurban named Rob as he comes to experience life in both worlds, uncovering truths and choosing sides in the process.
http://en.wikipedia.org/wiki/The_Guardians_(novel)
and the TV series
http://en.wikipedia.org/wiki/The_Guardians_(TV_series)