Cameron seems to be saying that the English language, architecture, art, history, literature and music have all been influenced by Chrisitianity. But who has ever denied that? Portillo's remarks are even more lame-brained. If "we all know" that you can't mention Christmas or send Christmas cards any more, he won't have any trouble reeling off a list of people he knows who object to the mention of Christmas or to people sending cards.
I also find it amusing that the Church of England is now reduced to being defended by a self-proclaimed "wishy-washy" Anglican PM who has said that his faith comes and goes like the radio reception in the Chilterns and a lapsed Catholic atheist.