The owner of Toblerone is taking legal action against a tiny British vegan chocolate brand which it claims has been copying the Swiss chocolate bar's famous chunky shape.

Mondelēz has filed papers at the high court in London accusing Catherine's Original's of "passing off" and trademark infringement with its O'bar – a length of chocolate divided into segments each with a rounded semi-oval hump.

The 200g bars cost £9.20 for a milk or plain variety, and as much as £10.55 for more exotic flavours such as pumpkin spice or cinnamon swirl. A standard milk chocolate Toblerone can be bought for £2.50.

Catherine's Originals, founded by the then teenager Catherine Dodd in 2021, makes its chocolate in Walberton in SussexEngland and sells them via markets, online or by subscription.

Dodd said the shape of her bars reflected an O for Originals. "We stand firmly behind the product and identity we've created," she said.

"We strongly disagree with the claim concerning O'bar and are working with our legal team to defend our position. Honestly, it's fairly frightening for a small business we've put so much care and hard work into building. But being a smaller business does not mean being afraid to stand up for what we've created."

The brand's legal adviser, Stephen Lowry, at Brandsmiths added: "Our client disagrees with the claim and considers O'bar to have its own distinctive design and identity. We look forward to addressing the matter through the appropriate legal process."

Mondelēz International, which also owns Britain's Cadbury brand and Côte D'Or coffee as well as Toblerone, said: "The iconic Toblerone shape is one of the most recognised and distinctive product designs in the UK and across the world, and has been a hallmark of the brand since 1929.

"We have a responsibility to protect our trademarks and intellectual property, which we take seriously. We have attempted to resolve this matter constructively and directly with Catherine's Originals over several months but unfortunately have been unable to reach an agreement. We cannot comment further on ongoing legal matters."

The latest battle over Toblerone comes after budget chain Poundland was forced to delay the launch of its Twin Peaks bar in 2017, which had two humps rather than the single peaks of Toblerone, after a legal warning from Mondelēz.

The bar eventually relaunched after Poundland modified the colour of the packaging and the shape of the bar and is still on sale today.