The Birkenstocks: A story of sandals, scandals and cellulite, in which an ex-husband and wife go to war over feet

The former wife of the heir to the Birkenstock sandal dynasty will travel to London next week to launch her own range of therapeutic but fashionable footwear. Susanne Birkenstock, the ex-wife of Christian Birkenstock, presents the Beautystep - a designer sandal with a specially contoured sole which, according its manufacturer, massages the foot, improves posture and reduces cellulite.

On the other side of the battle lines, meanwhile, the Birkenstock family is re-issuing one of its classic sandals, for which it makes a similarly ambitious set of health claims. The rival launches come after a bitter divorce and a lawsuit over the use of the Birkenstock name. Under the ruling, Ms Birkenstock can still use her married name to sell her shoes - on condition that it is printed at a distance from the Beautystep logo, and at one-10th the size.

With their chunky soles and thick leather straps, the two sandals are superficially similar, but each company says that its design is the result of scientifically rigorous - and carefully guarded - research.

"It is very important for me to make the difference clear between the Beautystep and the Birkenstock because I am presenting something totally new," said Ms Birkenstock. Her sandals are marketed under the brand S/B International, but Ms Birkenstock's surname is still peppered across the shoe's promotional material.

Despite the strict conditions imposed by the court, the potential for confusion remains, said Wayne Hemingway, the design and branding guru. "With her name on it, the public will think this is a high-end version of the Birkenstock. She'll be able to achieve a niche market of people that think it is a limited edition of the original," he said.

However, the Birkenstock name is so well established that it is unlikely to be threatened by its new competitor, he said.

But fashion commentator James Sherwood predicted that the fashion world's insatiable hunger for innovation will take the Beautystep straight to the A-list. "There will be snob value for her range because it's new. The fashion people will be on her side because it's new and it's going to be stocked in Harrods," he said. "But fashion people have been wrong in the past: in the summer you still see queues of people outside the Birkenstock shop."

According to Ms Birkenstock, the Beautystep was created to produce an effect similar to walking barefoot over soft sand. Its distinctive, curved sole causes the wearer's muscles to work harder, boosting blood circulation. The range is already proving successful in Germany and Austria, where 30,000 pairs were sold in the first three months, she said.

But Ms Birkenstock's plans to break into the UK market may be hindered by the family company's decision to re-launch its Noppy-flex range. Advertised as an "energising massage sandal", the footwear features a patented sole covered in rounded rubber nodules that massage the wearer's feet as she walks, said Dirk Fuhrmann, the creative director of Birkenstock UK. "They're like a home reflexology kit. You massage the pressure points just by walking," he said.

Although the Noppy-flex was originally designed in the 1970s, Birkenstock deny that the re-launch was timed to coincide with the emergence of a rival brand. "It's a product we've produced for years - we just decided that now would be a good time to push it forward," said Mr Fuhrmann. "We have been watching what Susanne Birkenstock is doing, but not with any great concern."

Both companies insist that the two designs will not be in direct competition.

This year's clash is the latest chapter in a story of marital strife, business rivalry and bitter court battles, which has racked the multimillion-pound sandal empire since Ms Birkenstock separated from her husband in 2003.

Before her divorce, the glamorous 34-year-old was credited with rescuing a once frumpy product and turning around the fortunes of a company that dates back to 1774.

Susanne was 15 when she met Christian and the couple married when she was 18. She joined the family business, and soon started experimenting with her own designs. At the time, the classic cork-soled Birkenstock had not changed since the company sold its first sandal in 1964. But when Susanne's creations were noticed by fashionistas such as Heidi Klum - the model agreed to design her own range - the brand was reborn as an iconic brand worn by stars such as Gwyneth Paltrow, Ewan McGregor and Leonardo DiCaprio.

After a traumatic divorce in 2004, Ms Birkenstock launched her own footwear company with a publicity campaign that leant heavily on her married name. The family was incensed, especially after receiving requests for her shoes from confused shop owners. Susanne countered that after 16 years of marriage - and the mother of Christian Birkenstock's two children - she was entitled to use her own surname.

An attempt to negotiate a settlement failed, and early last year the family filed a lawsuit at a court in Cologne, accusing Susanne of "sponging" off their brand name. The court ruled that Susanne could continue to use her name as designer, but imposed strict rules on how prominently it could be featured in promotional materials.

Christian Birkenstock said that he bore no ill-will towards his ex-wife, but he defended his decision to take her to court: "We Birkenstocks are a large family. There are a lot of us. But they can't all go around producing shoes, in the same way that people called Porsche or Mercedes can't all go out and make cars."

SANDAL WARS

'IoS' fashion writer Elisa Makin tests the rivals...

HIS BIRKENSTOCK

Noppy-Flex £29.95, by Birkenstock

This is similar to the firm's original sandal, with a buckled toe-bar on a wide, flat base. The main difference is the addition of a slightly scary-looking pimpled rubber sole that massages your feet as you walk. The emphasis of this sandal is very much on improving the health and circulation of the wearer, but don't try running for a bus in them.

HER BIRKENSTOCK

Beautystep, £69, by Susanne Birkenstock

A departure from the wholesome appearance of the Birkenstock. But the attempt at glamour - with a row of crystals on the strap - is a little clumsy. The chunky soles are thicker at the front and force you to stand straight. It doesn't feel quite like "walking barefoot in the sand", but they certainly tone the calf muscles.