You'll be relieved/sickened to know I've finished reading 50 Shades of Grey. I'm genuinely fascinated by this book's appeal because it's appalling. But lots of people (including cool, urbane sophisticates like me) are talking about it and even more people have really enjoyed the book(s).

Once I stop to think about that - and once I've stopped laughing - I have one question and one question only:

WHY??

Reader, I have theories.

1) Women like porn and they like talking about liking porn. They like giggling over the rude bits - I've heard them in Costa! - and they bond when they talk about it. Women are discovering that sexuality is a thing to be openly discussed/read. Judging by the enthusiasm with which I've heard women of all ages talking about 50 Shades, it's enabled them to talk about sex in a way they haven't before. (Or at least, they've never talked about it when I've been with them). I hate this phrase but it appears that through erotica like this, women genuinely feel a sense of 'empowerment.'

2) However poorly written, the book articulates female desire in a way that 'Confessions of a Shopaholic' just doesn't. It talks about what the heroine Ana wants, imagines and experiences sexually in explicit (albeit gratingly repetitive) scenes. Women can allow themselves to be turned on by written erotica in a way they can't with visual porn. Reading a rude bit in a book isn't the same as watching some drugged up tart getting banged twos up by a couple of midgets in a porn movie. (Just to be clear, I've never seen a porn film like that. I'm merely speculating on potential subject matter). Unlike a porn film, written erotica isn't exploitative so women can enjoy it with a clearer conscience than they otherwise might.

3) It talks about spanking. Maybe the BDSM thing gives the book a 'naughtier' edge? Perhaps darker fantasies involving dominance and submission speak to women on a deep level? I dunno - I'm theorising. I'm the kind of woman who thinks role play is the kind of thing you do on a customer care course. But surely spanking's got to contribute to the book's success, hasn't it?

4) Christian is a highly appealing fantasy figure. Personally, I couldn't stand the berk but women obviously love this character. Arrogant, supercilious and murmuring he really got on my tits - and not in a good way. He's an emotionally damaged billionaire with control issues - I imagine women want to serve and mother him at the same time. Like most (all?) romantic heroes, he's dark, brooding, misunderstood and seemingly unreachable. As an equivalent, imagine Emily Bronte's craggy Heathcliffe as a mega-rich sheep hustler, trying to spank Cathy every five minutes. As a literary formula, what's not to love?

5) Women use the book to explore their own imaginations. This gives women 'permission' to smuggle their own fantasies into their daily lives, find their boundaries and seek ways to express what tickles their fancy.

Adultshop.com, one of Australia's largest sex toy retailer, has said sales across the board were up an average 40% on last year. Sales of some toys and accessories - particularly those featured in the trilogy - have jumped by as much as 80% since the books came out.

At Babeland, an adult store in New York, sales of kinky products are up nearly 30% in the last few months and visits to the bondage section of their Web site have spiked by a spanking great 81%, reports the New York Post.

And it's not just sex stores benefiting from the buzz, but hardware stores (and in this case "hardware" simply means hardware) are also selling to a new class of customer -- women fresh from reading the books seeking out soft cotton 'bondage' rope. (I went to Homebase a couple of weeks ago for some WD40 but I haven't used it as a sexual lubricant - I had a squeaky hinge). Meanwhile, the uber conservative Brooks Brothers men's clothiers are capitalizing on their abruptly popular eight shades of grey neck ties.

If women are prepared to spend their hard (yes - harder, no - HARDER) earned cash on sex toys during the worst global economic downturn in human history, it suggests they're desperate to get their kicks. Maybe the 50 Shades phenomenon is so big BECAUSE of the global economic downturn - maybe women are feeling so damn pissed off with life they're more up for a bit of the other because everything else is so bloody depressing. Maybe against the backdrop of redundancy, penury and fear, reading a mucky book is just the kind of escapism women need right now.

Incredibly, 50 Shades Of Grey and the other two books in the trilogy have collectively sold more than 1.5 million copies in the past 15 weeks, obliterating the speed of sale of past blockbusters like the Harry Potter franchise and The Da Vinci Code.

Apparently, most buyers are middle aged women.

*short pause while that rather embarrassing fact sinks in*

For me, I thought the book was one of the most badly written piles of shite I've ever read. I didn't find it sexy but then again, I find James May quite sexy so that tells you a lot about my personal taste. But it can't be denied that people love this book and it's a huge commercial success - something every writer longs for, no matter how snobby they might say they are about "selling out" to go "mainstream." So hats (and pants off) to E L James.

Betcha sales of AA batteries have gone up as well...

(Just to point out, I'm not sure if sex toys require AA batteries. That was just a wild stab in the dark...)

Follow Emma Clarke on Twitter: www.twitter.com/emmabclarke