Have you found that your dress size has shrunk over the past decade while your shape and weight have stayed essentially the same? If you consider yourself a size 14, why is it that you feel excluded by designer fashion boutiques whose size 14 clothes are too tight? If these inconsistencies ring true to you, then you are a victim of “vanity sizing”.

Vanity sizing is a retailer or designer’s way of making you feel better about yourself by putting a smaller size on the label than you actually are. So no, it’s not you who has shrunk, it’s the label that is lying. Vanity sizing is a device used by shops to sell more clothes, and to create loyalty so you keep coming back to them. It is a practice so widespread throughout the fashion industry that most shoppers accept that negotiating size inconsistencies between stores is built in to the shopping experience. “I definitely prefer to shop in stores where I am a size 12. Though in designer clothes I’m a 14,” says TV researcher Sophie Reid, 23. “So obviously I shop where I’m a 12, and avoid the places that tell me I’m a 14. But when I fit a size 10, as I do in some things at Principles, then I just get suspicious that they are trying to con me.” Reid’s experience is common. Just over 60 per cent of women admit they are unsure of their dress size, such is the variation from store to store, according to results from a three-year survey conducted by SizeUK, a collaboration between the government, 17 major British retailers and leading academics and technology companies.

Over the past few years the practice of vanity sizing has sparked a raging debate in this country over women dieting to fit certain dress sizes – think zero, and double zero. “Vanity sizing is all about making women feel thinner than they are. We want to wear brands that flatter us. We have stocked size zero, or UK size 4 clothes at Browns,” says the store’s fashion director Yasmin Sewell, “and we sell them to petite women. We also work with several celebrity stylists who practise vanity sizing to keep their A-list clients happy. They will cut out a size 14 label and sew in a size ten label. It’s the same thing.”

Designer labels vanity-size too, for different reasons: their own vanity. Have you ever wondered why designer labels do not offer clothes above a size 14? “Designers size their clothes meanly because they want to keep big people out of them. Having fat people wear your clothes is not good for a brand’s image. It’s a fact of life,” says Brix Smith-Start, former guitarist with the Fall and owner/buyer of Shoreditch designer boutique Start. “Miu Miu, for example, is very mean on its sizing. Its size 10 is smaller than Chloé’s size 10. Miu Miu doesn’t want heavier people wearing its stuff because beautiful people perpetuate the myth that only beautiful people wear the clothes. If you are curvy and have an arse – forget it.” Even outsize retailer Evans practises a form of vanity labelling. Look inside the clothes and you won’t find the word Evans on the label, just an anonymous logo. Even big women don’t want their clothes to tell them they are big.

According to the designers spoken to for this story, labelling clothes as smaller than its actual measurement is intentional. “Most high street stores vanity-size,” says one high-street designer. “It’s endemic, but we do it to make customers feel good about themselves.” In the case of designer jeans, on a visit to Selfridges’ denim department, one woman looking for the perfect pair found that every single brand tried was, when tape-measured, incorrectly sized. The worst offender was a pair of 26in-waist Rock & Republic jeans that actually measured up as a 33.5in waist – a difference of 7.5in. Nonetheless, our tester was ecstatic to have a pair of 26in waist jeans on, even if she in fact has a 31in waist. Every other jean label measured, from Cavalli to Diesel, had some discrepancy from size to true measurement.

I believe myself to be a size 10. At Topshop and from most designer labels I am a 10. So just to confirm that vanity sizing is alive and well on the British high street, I tried lots of black trousers in a size 10 from the high street. The fits, as you can see from the photos, are varied to say the least. Topshop fitted like a glove. Gap and Marks & Spencer’s were falling off. Hobbs’ trousers fitted on the waist but were massive on the hips.

If you’re wondering how stores can get away with this, the answer is easy. Put simply, clothing sizes in this country are not and never have been standardised – so, strictly speaking, definitive dress sizes don’t actually exist. Yep, I was pretty surprised, too. This may change next year if the European Union succeeds in introducing a universal sizing system which will state measurements in centimetres – but right now retailers can put pretty much any size they think is relevant on the label of their clothes.

So, sizes don’t exist as such. But herein lies the problem. Size does exist – in our minds. We base our perceived dress size on the only official data readily available on women’s clothes sizing, which is so out of date – a mass measure in 1952 – as to be risible. Yet it is the results from this survey relating a bust, waist and hip measurement to a specific dress size – a 12 was decreed to be a 34-26-36 (my size today, incidentally) in 1952 – that most British women have locked into their heads as the “truth”.

The upshot of this is that sizes 8, 10 and 12 are seen as aspirational, and 14 and above as “bad”. Rationally (but who is rational about weight?) this is balderdash. What we should be aiming for are clothes that look good on the body. Damn the size.

But it doesn’t work like that. The most up-to-date data on the real size of the nation is available from SizeUK. In 2004 SizeUK delivered the results of the first national survey on the shape of the British nation since the Fifties. The data from this survey conducted using the Bodymetrics 3D body scanner (the same device that helped our tester to find jeans that fitted at Selfridges) took 130 individual measurements from 11,000 people. The data is, of course, available only to those who can afford it – indeed those who funded it – namely mass-market retailers.

The survey revealed that body shapes and proportions have changed dramatically since the Fifties – and guess what? We’ve all gained weight, with British women adding on average 2.5in around the hips and 6.5in on the waist, and gaining 7lb. The average British woman now measures 39-34-41. There’s no measurement for a definitive size 12 though, or any other size. And questions beyond that (which city in the UK is fittest? Are northern women fatter than southern? Where are the skinniest women?) are met with a wall of silence from the SizeUK people.

What SizeUK did was to provide measurements of the population according to age and where they live, which could then be tailored by individual stores to suit their customer base. This demography-style sizing provided just the right ammunition to retailers so they could update their size charts and create clothes that satisfy the size and shape of their target customers.

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