Mind you, the official Census numbers from 2001 say that 73 per cent of British people identify as "Christian". However, this is probably due to a leading question on the Census form. "What is your religion?" it asks, which seems to assume that you must have one - especially since it follows a section on ethnic origins, and we all have those.
So a lot of people put down Christian just because that is the ancestral religion of their family. Make the question "Are you religious? If so, what is your religion?" and the result would probably be very different.
There were attempts to get that more neutral question on to the 2011 Census form, but churches lobbied frantically against it. They are feeling marginalised enough as it is.
Why would David Cameron proclaim the virtues of a Christian Britain that no longer exists? He is no religious fanatic; he describes himself as a "committed" but only "vaguely practising" Christian.
You'd think that if he really believed in a God who scrutinises his every thought and deed, and will condemn him to eternal torture in Hell if he doesn't meet the standard of behaviour required, he might be a little less vague. But he doesn't really believe that he needs religion himself; he thinks it is a necessary instrument of social control for keeping the lower orders in check.
This is a common belief among those who rule, because they confuse morality with religion. If the common folk do not fear some god (any old god will do), social discipline will collapse and the streets will run with blood. Our homes, our children, even our domestic animals will be violated. Thank god for God.
Just listen to Cameron: "The alternative of moral neutrality should not be an option. You can't fight something with nothing. If we don't stand for something, we can't stand against anything." The "alternative of moral neutrality"? What he means is that there cannot be moral behaviour without religion - so you proles had better go on believing, or we privileged people will be in trouble.
But Cameron already lives in a post-religious country. Half its people say outright that they have no religion, two-thirds never attend a religious service, and a mere 8 per cent go to church, mosque, synagogue or temple on a weekly basis. Yet the streets are not running with blood.
Indeed, religion may actually be bad for morality. In 2005 Paul Gregory made the case for this in a research paper in the Journal of Religion and Society entitled "Cross-National Correlations of Quantifiable Societal Health with Popular Religiosity and Secularism in the Prosperous Democracies: A First Look."
Sociological gobbledygook, but in a survey of 18 developed democracies, Gregory showed that "in general, higher rates of belief in and worship of a creator correlate with higher rates of homicide, juvenile and early adult mortality, [venereal disease], teen pregnancy, and abortion".
Even within the United States, Gregory reported, "the strongly theistic, anti-evolution South and Midwest" have markedly worse crime rates and social problems than the relatively secular North-East. Of course, the deeply religious areas are also poorer, so it might just be poverty making people behave so badly. On the other hand, maybe religion causes poverty.
Whatever. The point is that David Cameron, and thousands of other politicians, religious leaders and generals in every country, are effectively saying that my children, and those of all the other millions who have no religion, are morally inferior to those who do. It is insulting and untrue.