Arabella Weir: I can choose not to be fat. But not everyone can

You know that trap that famous people often fall into when they're riding high? The one when they say something phenomenally stupid because they're so blinded by their own current popularity they forget it all hangs on a thread, and that any wrong move can turn you from, say, Chris Rock into Chris Martin in the blink of a faux-pas?

For example, I'll never forget seeing that almost-sweet-he's-so-stupid village idiot Peter Andre commenting on his multi-bejellewed waistcoat in the documentary Katie and Peter: The Wedding saying to camera, "I think people like me and Katie because although we like bling we're also very classy".

From the mouths of babes. It would appear that Dave "ordinary bloke" Cameron has careered headlong into that trap too. Speaking oh so bravely out against "moral neutrality" he invites us to tell fat people that it's their fault they're porky, poor and unemployed. 'Ave that, you pikey! Get in my son! You tell 'em, Dave! Man, he's fearless, isn't he?

Here he is having a go at those who were never going to vote for him anyway and who are so disenfranchised that they're as alien to most of society as fairground freaks. Clever, eh? See what he done there?

Sure he gives a nod to social circumstances: "Where you are born – your neighbourhood, your school and the choices your parents make – have a huge impact," Cameron generously concedes "But social problems are often the consequence of the choices people make."

Doh, like, really? Like choosing to be born into a poor, woefully under-educated family to parents who didn't chose to send their kids to leading public schools. Those kinds of choices? Or maybe he means choices like not getting a job in the area you live where there's endemic, long-term unemployment?

Or, hey, maybe he means choices like being a mother who has failed to "compel the father of her children to stay", as he recently suggested was at root for the prevalence of single mothers. What on earth could he possibly know about choices apart from those available to all us with money, opportunities and privileges?

He's not entirely to blame, though. Dangling the highly seductive notion of choice wasn't his idea. It was Tony Blair's. And it was a stroke of genius. Suddenly everyone was being told that they, just like toffs, could choose – choose schools, doctors, surgeons, treatments. How do you go about choosing when you don't have the necessary tools such as education and privileges to exercise choice?

You might as well tell me I can choose to do my own plumbing. A super empowering notion, sure, particularly when I've waited three weeks for one, but without the all the equipment it's just that – a notion.

Grasping the nettle, Cameron kept wading in. "We talk about people being 'at risk of obesity' instead of talking about people who eat too much and take too little exercise." Of course you're bleeding well "at risk" if you come from the socio-economic group most likely to eat badly as a result of being less well versed in good eating habits and with the least access to shops selling quality food at reasonable prices.

Take me, for example. I'm a bit fat. Now, as Cameron suggests, I can choose not to be fat. As it happens, I actually can. I can afford a cleaning lady twice a week, and regular, reliable childcare. I have a supportive husband who organises his work to ensure he's with the kids as much as I am. I work in a well-paid industry where, in the main, I dictate the hours.

So, without any of the onerous, relentless, ordinary burdens of being a working mother I am freed up to go out running four times a week. I'm not getting any thinner but I'm definitely fitter. Mmm, Dave, I'm still a bit fat, though. Got any ideas?

Oh, while we're at it, I'd better confess to drinking more than is officially advisable for women. My fault, again, definitely. I can afford nice wine and my life isn't so without hope that I need to drown my sorrows in a bucket of Special Brew every day so we're all right, for now. Who knows where I'd be if I'd been born in Glasgow East, for example, where a man's life expectancy is 61. Try telling him and his family their circumstances are their fault.

Most pernicious, however, were Cameron's comments "that society had been too sensitive in failing to judge the behaviour of others as good or bad, right or wrong". Who among us would dare to judge a person's size, employment status and financial situation without knowing that individual's full background? Only someone stupid, vain and in hot pursuit of tab loid headlines – someone like, erm, Peter Andre or David Cameron. It's hard to decide which one of them is less in touch with reality.

Arabella Weir's next book, 'Fat Girl Confidential', is out in 2009