Rhiannon Harries: It's a tall order to look like a model, no matter what they're wearing

With the spring/summer 2010 round of catwalk shows now well under way, anyone who regularly picks up a newspaper, browses the internet or switches on the TV can expect the biannual deluge of images of lithe young bodies stalking the runways. Cue much body-envy and self-hatred among 50 per cent of the population.

Time spent envying others is, of course, a complete waste of one's numbered hours on the planet. The only thing that trumps it in the pointless pastime stakes is misdirected envy, which is why I am always surprised by the reactions of my peers while flipping through the glossies' seasonal trend reports.

Typical comments are usually of the "Of course you can wear those thigh-high Prada waders if you are six foot tall..." or "God, imagine having the legs to pull off that crotch-length Balmain number!" variety.

If you've never heard this stuff first-hand, then I'm sorry to introduce you to a sad side of human nature, but trust me, it exists. Baffling, but only because most women miss the point when they fantasise about looking like supermodel Natalia Vodianova in the latest Chanel couture.

The real advantage of thinness in the world of fashion works at a much more humble level. Yes, a size-zero figure will probably mean that you look fabulous in sample-size YSL, but what is really enviable – and far more relevant to most of us – is how fabulous it will also probably mean you look in New Look and Primark.

Expensive clothes look sublime on tall, willowy girls, but most also look surprisingly great on everyone else thanks to good cut and quality fabric. Cheap clothes, meanwhile, are rarely forgiving on those of us who actually fill them – a bulging seam is a lot more likely to reveal how shoddily it has been sewn. The bottom line is, it's a hell of a lot easier to look good on a budget if you're thin.

It's something that always springs to mind when the idea of a "fat tax" rears its head from time to time. I don't suppose many great economic minds of the day are currently beavering away on the question, but I wonder how much of the money that obesity-related illnesses cost the NHS is ploughed back into the economy by women whose endless high-street sprees are basically just a quest for that elusive garment which will disguise an extra half-stone.

So, should you ever find yourself sighing wistfully over a picture of Kate Moss, remember: just because she's thin doesn't mean she's better or happier than you. It just means she gets a hell of a lot more for her money at H&M.