Birkenstocks step back into the fashion limelight

First there were "nan shoes", "chunky sandals" and "pool sliders". But this summer's trend for ugly shoes has spawned a footwear movement all of its own, as the Birkenstock sandal steps up again. Despite being 50 years old, vegan-friendly and politically charged – American conservatives coined the pejorative term "Birkenstock liberals" in 2004 – the German orthopaedic sandal is proving to have more fashion staying power than Kate Moss.

The distinctive cork-soled sandals, first produced by Karl Birkenstock in 1964, are selling out across UK retailers. Amazon.co.uk's shoe store reports a 95% rise in sales of all varieties of the sandals in the last few weeks, while Asos has had similar success.

"The key style for us has been the Arizona [two-strap] in black and white, which is flying out," said Hayley Beech, worldwide buyer for Asos. "We have stocked Birkenstock for several years, but they have had an amazing season on Asos for spring/summer, with a huge sales increase on last year. We have had to do multiple trade repeats this season as the demand is so high."

The shoe is also popular at the luxury end of the market. "Birkenstock has done very well this summer. The blue-and-white stripe and navy colour sold out very quickly. We bought in the red, black and white solid colours, which came in a fortnight ago and have already sold out," said Natalie Kingham, buying director at luxury online retailer Matches Fashion. "Clients are looking for summer footwear options that are more grounding, that can be worn with a summer dress but which have a bit more attitude."

Birkenstock's two-strap Arizona is the style du jour, having made an appearance in the Céline spring/summer 2013 collection in Paris.

"That silhouette was universally considered ugly," Vogue contributor Katherine Bernard told the magazine in July 2013. "But [Céline designer] Phoebe Philo's luxe reinterpretation got me thinking. It's the most comfortable sandal in the world having a stylish renaissance."

Givenchy has also produced two versions of the Arizona sandal, one floral and one metallic, retailing at £545 and £595 respectively. The original Birkenstocks, at a rather more accessible £49.95, have enjoyed knock-on success as a result of their high-end brethren.

"Have they ever come back in fashion?" asked Robert Lusk, founder of the Natural Shoe Company, which owns the Birkenstock UK flagship store in central London. "To be honest, demand is so huge this year that we can't meet it. We've got workers pulling all kinds of shifts. They've pulled out all the stops to meet demand."

There are now 800 varieties of Birkenstocks, from triple strap to the thong, and more than 12m pairs were produced for the global market this year. The London flagship store recently underwent an overhaul, transforming the 600 square feet space to include iPads to enable customers to order online should their preferred model not be available in the shop.

Like all good family dynasties, the Birkenstock clan have had their hiccups. In 2004 a "sandal war" erupted when Susanne Birkenstock, separated from her husband, Christian, began producing high-heeled sandals, called the Beautystep, using her married name. "Beautystep is a nice name; I hope she sells a lot of product," Christian told the Guardian in 2005.

"The only problem is she has to leave the name Birkenstock off the shoes. People were telephoning our stores and saying, 'Oh, you've brought out a new range of sandals.' But we hadn't – she had. That's why we had to send letters to the shops explaining that they weren't Birkenstocks."

But the Birkenstock's longevity, usually underscored by a growth of 10-15% annually, is most notable for enjoying fashion revivals on roughly a 10-year cycle. In the 1990s the sandals became part of the Grunge aesthetic; Kate Moss wore a white pair of Arizona Birkenstocks in the now-infamous Corrine Day photoshoot for the Face magazine in 1990.

In the early 2000s, the style was reprised once again by a number of celebrities – a Guardian article from 2003 mentions Jude Law, Jade Jagger and Gwyneth Paltrow as wearers.

Lusk is philosophical about the Arizona design being replicated by other designers, not least because it has had a dramatic effect on sales of the original. "The two-strap Arizona silhouette is universally known, it's an iconic design. I was in Italy a few years ago buying a motorbike and I met this wonderful Italian family.

"The women asked what I did and I explained. Her husband asked her to translate and she just leant over and made the pattern of the two straps across her foot, and he understood straight away. That was a nice moment."

Not bad for a German orthopedic shoe that Lusk recalls was initially met with derision. "People laughed at them at first, they thought they were funny looking. But we've got the last laugh now, as they say."