It really depends on what he exactly means by the word "christian". If you rip out the old testement, rip out the letters after the gospels and cross out some of the 'miricles',(most can be written off atleast as generosity or conjurers tricks) atleast the ones without any reasonable explanation then you are left with something that is atleast half-reasonable.

Of course England is Christian in the same Way that America is "Secular", oh and there actually is a state church so technically he has said something that is pretty much true. Anyway Whos to stop us Athiest's from being fans of jesus? I am all for more love in the world.

Just remember that England actually has a state Church which actually has a kind of strange nullifying effect on how much people care for the religion. Mostly it's just weddings, funerals and christenings and the rare hop in for christmas or rememberance sunday...Most people don't care and david Cameron's opinion will not change anyone's mind.