This is a response to this article, which was published in the Guardian on 2nd June. You don't need to have read the article beforehand though.
Mary Douglas may well have made the point that the food laws in Leviticus are all to do with category violation - aquatic animals that have scales are "clean" or kosher, aquatic animals that don't have scales aren't, and so on. It was common teaching in a strongly conservative evangelical church I attended from 1996-2000 when we did a series on Leviticus too, so it's hardly an insight the conservatives ignore.
Where Ms McGrath is less orthodox in her understanding of the Bible is in linking the rules in Leviticus to a "huge anxiety" arising from things being out of place. To do so is to assume that the Scriptures, including the food laws of Leviticus, are not inspired in the sense that is traditionally understood. It is quite possibly an intellectually legitimate understanding, but it is not an evangelical understanding of Scripture.
Contrast the more conventionally evangelical take on this (and yes, the irony is deliberate). Isaiah picks up the same theme in his first chapter:
Hear, O heavens! Listen, O earth!
For the LORD has spoken:
"I reared children and brought them up,
but they have rebelled against me.
The ox knows his master,
the donkey his owner's manger,
but Israel does not know,
my people do not understand."
Isaiah 1:2-3, NIV
We are the category violators. Everything else in the universe obeys God and belongs to the place it belongs to. But people don't. We don't know the God who made us, we don't obey him, even though the observed laws of nature testify to the universe always obeying God.
But Jesus did obey God. He was the only person who was not a category violator - the only person who was intrinsically clean, the only person who lived in obedience to God. And so he was crucified, not as a category violator when surrounded by non-violators, but as the only category keeper surrounded by violators.
We don't make the categories. God does.