Bottom line is that Derbyshire believes that Christianity is a good thing generally, and definitely a benefit to the West. I’m an atheist in the Derbyshire mold, which is why, like him, I support Santorum, the most openly-religious candidate in the GOP field. He’s a nag, but there’s nothing wrong with being one, given the tendency of modern churches towards cargo cult Christianity (prosperity gospel and mid-level marketing like heresies). In a world where the traditional virtues are being given short shrift, someone needs to make the case that libertinism and the shucking of personal responsibility are a dead end rather than the way forward.
I understand the concept, and I saw it often in the older generation with conservative “cultural Catholics,” and secondhand was aware of it with Korean Buddhism, in which more conservative older people accepted the religion as providing a moral foundation for society and might participate to one extent or another while being agnostics or atheists. My impression, for better or for worse, is that Derbyshire’s approach to religion was rather common in the older generation of British conservatives.
I've been saying for a very long time that the division between economic, national defense and social conservatives does not need to be as bitter as it has become. The older type of political conservative, even if he didn't personally believe, thought that being a good American (or good Englishman) included at least formal support for the church and not openly attacking morality. It sounds like Derbyshire falls into that older model of conservative.