On Kindles, iPads, and plain old-fashioned books; in posh papers, the tabloids and on radio phone-ins, sun loungers and public transport, there is one cultural phenomenon that it's no exaggeration to say has gripped the nation (or at least its female half): the Fifty Shades trilogy by the previously unknown British author E L James.

The first book is the biggest-selling British novel aimed at adults, with UK sales of 2.3 million since April, and 20 million for the trilogy already in the US. Ahead of James in the UK are books aimed at children like Harry Potter and overseas authors: Dan Brown, Stephenie Meyer and Stieg Larsson. Fifty Shades of Grey is now the UK's fastest-selling book ever (beating Potter), so it is a safe bet that many more records will fall. The movies, first details of which emerged yesterday, will be huge.

How depressing! Not because of any snobbish disregard for James's writing, so scorned by jealous critics. Not because of all the "better" books that eke out a tiny fraction of Fifty Shades' sales. No, the real problem lies in its message.

The casual normality of BDSM at the heart of this story would worry me even if I were not the father of two teenage daughters. Thousands of girls, many of them pre-sexualised, have read this book, most (thanks to digital devices) without their parents' knowledge.

It's different to Twilight. They all know vampires aren't real. But Christian Grey plays into modern pop culture's ideal of the desirable man: drop-dead handsome, rich as Croesus, if not Bob Diamond, and totally in control. Why, he even flies his own helicopter. So far so mainstream (however objectionable). It's the idea that submission to violence and domination is part of the attraction that is so worrying.

In James's defence, she did not know it would be read by an entire generation, and I would be the last person to advocate any attempts at censorship, or even squirting HP sauce at women reading it (see yesterday's i), doomed as they would be. And, I know, I know we get the culture we deserve, and no one forces us to buy it. BUT... the message of the book really is Fifty Shades of ("Holy") Crap.

And, yes, I have read it.