Tall to petite: Why does the British high street do 'niche' fashion sizes so well?

According to the UK's last National Sizing Survey, the average British female is 5ft 3.75in tall and weighs 10.25st. She has size six feet, a 34in waist and 40in hips. As a woman who stands at well over 6ft and has boats for feet, I've spent a lot of my life longing for those measurements. Imagine seeing that perfect pair of boots and actually knowing you'll be able to get them in your size. It's the stuff of dreams.

But gradually, over the past decade, things have improved. Where once I had Topshop's tall range and the middle-aged selection at Long Tall Sally, I now have what feels like a whole high street to choose from. New Look, Dorothy Perkins, Next, Very, Marks and Spencer and many more now cater for taller figures and there are even more stores with petite and plus-size ranges too.

And, to add to the list, the online clothing store Asos is about to launch its very own tall range. When this news was announced on the Facebook page for All the tall things – a blog about fashion for tall women – the readers were giddy with excitement. "This is the best news ever, although I'm sure my bank manager is already crying," said one commenter. What's interesting is that I so rarely see women on my eye level walking the streets of the UK, yet I find it fairly easy to find clothes that fit.

The plus-sized market is a well documented phenomenon, but the other categories that count as niche sizes – petite, maternity, plus-sized jewellery, wide-fit shoes, tall – aren't discussed as much. Yet for some reason British high-street stores are catering for them all more than ever. Why does it make good business sense? Jacqui Markham, design director at Asos, says that part of the decision to introduce niche size ranges is the international nature of its customer base. Asos has nine local language websites, from German to Italian. If they're going to attract 6ft-tall Petra and 5ft-tall Isabella alike, a larger range of sizes is required.

Jessica Fioriti, retail analyst at Verdict Research, says the decision by retailers such as Asos to focus on niche sizes is partly an attempt to find new ways to compete. "Womenswear is a very mature market in the UK, so it is difficult to achieve sales growth organically through fashion-led ranges or by lowering your price points alone."

Though niche size ranges may not contribute to a large number of sales, they are useful for customer loyalty. Fioriti says that part of the calculation is that if a customer chooses a retailer because they sell jeans in the unusual size they need, they may also buy bags, shoes, and other categories of goods. And the ecstatic reaction on tall fashion blogs to the news that Asos would launch a tall range demonstrates the depth of gratitude you can feel towards a brand that sells trousers that are actually long enough.

Fioriti is clear that niche sizing is something that other countries aren't embracing to the same extent. The general importance of sizing to mainstream retailers seems to have increased with the rise of internet shopping, something the British have embraced more than most. A 2013 survey from Ofcom found that UK shoppers spend more online per person than any of the other major countries surveyed – £307 per head more than Australia, which was the second highest for online spend, and £615 more than the overall average spend.

"Fit has become a lot more important [in British retail] over the past 12 months," says Fioriti, a trend she thinks will continue. "Consumers can justify a purchase online if they know a product will fit well."

Whatever the reasons, the trend among British womenswear retailers to cater for niche sizes is making various small groups of people very happy. And everybody knows that happy customers are good for business.