Look at the winsome lady to the right. It’s the actress Maggie Gyllenhaal, Jake’s big sister, and doesn’t she look pretty? All knowing smile and dancing eyes, she’s like that sixth-former you used to see parading around school like she owned the place, trailed by an army of adoring minions. But what’s Maggie, a bluestocking type, doing modelling satin basques? If you asked the average bloke in the street who they would want to see in their undies, she wouldn’t be top of the list. She’s comely but somewhat unconventional, and even Agent Provocateur – for which she is appearing in a new book of erotic fiction – admits she isn’t obvious man-magnet material. “We’ve always been mindful to create a brand that appeals to both men and women,” says Serena Rees, the co-founder of Agent Provocateur. And so they have. These pictures acknowledge the fact that girls fancy girls.

Oh, ladies – but we do, don’t we? We don’t talk about it much – even to our closest friends. But most of us, and I speak here of girls who generally like boys more, have, at some point, harboured a furtive crush on another woman.

When I was 11, I met a girl from the lower fifth at a swimming gala and, probably because she spoke to me, immediately developed an uncontrollable admiration for her. That night, in a bedroom covered in Smash Hits posters, I wrote in my diary: “She’s so beautiful and cool and I love her. But it doesn’t mean I’m a lesbian.”

What I didn’t get then is that girl-fancying has zero to do with the hot lezzer lust you see splashed on the cover of Nuts. That’s just crude male titillation – and girl crushes aren’t about men. In fact, with the possible exception of Scarlett Johansson, it’s rare that the sorts of girl we fancy are the same ones as the lads do.

The girls we’d go gay for aren’t the idealised versions of womanhood that men get off on – they are super-improved versions of ourselves. They’re the sort of female we want to hang out with and even want to be – in the way they dress, what they say and what they do. Angelina Jolie is a top girl crush because she’s powerful, in charge of herself and a wildcat with a sapphic past – but she’s too much for some men.

We’ve always hero-worshipped Kate Moss, but a lot of blokes think she’s scrawny.

The new girl crush on the block is the 23-year-old Lovefoxxx, from the Brazilian rock band Cansei de Ser Sexy. She cavorts on stage in stripy jumpsuits and cut-off jeans, and her body isn’t a perfect 10, but so what, when she expresses herself with such joyful abandon – and wouldn’t it be nice to have some of it, in more ways than one?

Yes, ladies, crushes are all about you. They are about the private and complex you that men – bless them – simply don’t get. This is why your object of desire won’t ever be just pretty. She will also have an interesting mind (or at least appear to, by wearing stylish hats) and a big, preferably torrid, back story, and, crucially, she’ll be too busy being awe-inspiring to care much what you think of her.

The thinking woman’s crumpet is much more compelling than just crumpet: Dorothy Parker, Emily Brontë, Zelda Fitzgerald, Colette, Sylvia Plath – these women were as unfathomable and brilliant as we sometimes like to think we are. And because they were clever, they were also out of reach – even in their lifetimes. Enigma is a critical crush ingredient. That’s why you hope not to bump into your favourite sixth-former 15 years later, plump and harried, pushing a buggy through Tesco.

Of course, the critical question actually is: would we go there? Stories about clandestine sexual awakenings are very erotic – oh, Anna Friel in Brookside! Oh, Hilary Swank in Boys Don’t Cry! But if Maggie G turned up on your doorstep promising to take you to places you’d never been before – yes or no?

Some of us would and have. And some of us are scaredy-cats and, whatever we tell people when we’re drunk, would probably just rather think about doing it than make the leap from fantasy to flesh. Sienna Miller and Keira Knightley are about to reignite the whole question in their new movie The Edge of Love, in which they play the lovers of Dylan Thomas. The girls have started the titillation early by appearing together everywhere, hand in hand. Are they or aren’t they?

Maybe it doesn’t matter. Maybe crushes are best left as vaguely disquieting feelings that tell us more about who we are than what we think about others. As private daydreams, they’re the last piece of our sexuality that properly belongs to us.

Lessons in Lingerie, is part of a collection of books entitled The Adventures of Miss AP. To see the whole saucy story, go to www.agentprovocateur.com

From The Sunday Times