Princess Leia from <i>Staw Wars/i>.

Carrie Fisher as Princess Leia in Staw Wars.

My son takes his birthday parties very seriously, with the planning for his forthcoming celebration usually starting the day after his last party has finished. This year he wanted a Star Wars theme, which was a relief to me because outer space is easy. Hand him a toy light sabre, put him in his dressing gown and you've got yourself a satisfied seven-year-old. Cake-wise, I bedazzled our young guests with an uneven slab of sponge smothered in lurid green icing. Jabba-the-Hutt cake, I told them, and they dutifully gobbled it, blind to the fact that it looked more like a sugary dinosaur booger.

The dress-up part was trickier for my daughter. There aren't many women in Star Wars. If you count the three recent movies then there's Queen Amidala, but all she does is sit around in an absurdly large headdress looking miserable. When it comes to females with spunk, there's really only Princess Leia.

The down side with Leia is her hair. Do you realise how difficult it is to sculpt those trademark buns? Even in a galaxy far, far away, women are apparently still oppressed by gruelling grooming regimes.

In 1985 the American cartoonist Alison Bechdel devised a test to check the gender bias of a film. To pass Bechdel's test, a movie must feature at least two female characters, they must talk to each other, and it must be about something other than a man. Star Wars fails this test miserably, but that's not surprising, as the majority of Hollywood films also fail.

However, there's something else that bugs me about Leia's role in Star Wars. As most readers would know, Darth Vader immediately senses that the Force is strong in Luke Skywalker. He can feel it, even at a great distance, partially because Luke is positively oozing the stuff, but also because Vader is Luke's father. Famously, it turns out that Leia is Luke's twin sister and is, therefore, also Darth's child. And we're told that the force is also strong in Leia.

So why does Vader never notice Leia's force? Was he distracted by her hair? But then what about the good guys, Obi-Wan and Yoda, who are already in the know about Leia's lineage? Why don't they attempt to train her in the ways of the Jedi? Unlike Luke, she's on hand, clued-up on intergalactic politics, and is all ready to fight; a perfect candidate for saving the galaxy.

What bugs me about all this is not that the film contains a sexist plot hole, but the fact that so few people even notice it. After all, the moment when Darth becomes aware of Luke's power is a vital story-point. And Star Wars fans have spent millions of nerd-hours poring over and analysing the film's every detail, looking for inconsistencies and mistakes. The fact that this gaping hole is so rarely detected, much less commented upon, suggests there's a deep, unconscious cultural bias at work. When a woman is passed over, when her power is ignored in favour of a man's, we hardly even notice it.

This bias may be subtle, but it's also profound. On the day of the party my yard was filled with little Lukes, tiny Obi-Wans, a couple of diminutive Darths, and even one very cute Yoda, all leaping about with their light sabres, battling and adventuring. Yet when I tried to hand a light sabre to my daughter she refused. Leia doesn't have one, she correctly insisted.

As far as my daughter was concerned, the really important thing about Leia was her hair. Which goes to show that at the age of three she has already absorbed the key cultural message. It's the boys who are called upon to save the day, while the girls have to make do with fancy hairstyles.

We might spruik the rhetoric of gender equality, telling girls that they can be anything they want to be, yet what they see all around them are strong, capable women still in figurative chains, still wearing figurative bikinis, dancing for the Jabba the Hutts of the world.

As I put my daughter to bed that night I told her my version of the Star Wars story; that Leia did become a Jedi Knight after the end of the last movie, and that she went on to conquer the universe. And the fact that her powers had been overlooked for so long? That just meant that she took all those Jedi blokes by surprise, and light sabred them right where it hurts. If only it was so.

Follow Monica Dux on Twitter @monicadux