The company behind Toblerone has started legal proceedings against a small British vegan chocolate maker, alleging that one of its products imitates the Swiss bar's well-known chunky shape.

Mondelēz filed papers at the high court in London accusing Catherine's Originals of "passing off" and trademark infringement. The dispute centres on the O'bar, a length of chocolate split into segments, each topped with a rounded, semi-oval hump.

The O'bar comes in 200g sizes and sells for £9.20 in milk or plain varieties. More unusual flavours such as pumpkin spice or cinnamon swirl cost up to £10.55. By comparison, a standard milk chocolate Toblerone retails for £2.50.

Catherine's Originals was founded in 2021 by Catherine Dodd, who was a teenager at the time. The business makes its chocolate in Walberton, Sussex, and sells through markets, online and by subscription.

Dodd said the shape of the bars was meant to represent an O for Originals. "We stand firmly behind the product and identity we've created," she said. She added that the company strongly disagrees with the claim and is working with its legal team to defend its 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 of Brandsmiths, said the client rejects the claim and believes the O'bar has its own distinctive design and identity. He said the company looks forward to addressing the matter through the appropriate legal process.

Mondelēz International, which also owns Cadbury in Britain and Côte D'Or coffee, described the Toblerone shape as one of the most recognised and distinctive product designs in the UK and worldwide, and a hallmark of the brand since 1929. The company said it has a responsibility to protect its trademarks and intellectual property.

It said it had tried to settle the matter constructively and directly with Catherine's Originals over several months but had been unable to reach an agreement. Mondelēz said it could not comment further on ongoing legal matters.

This is not the first time Toblerone's shape has been at the centre of a dispute. In 2017, budget chain Poundland had to delay the launch of its Twin Peaks bar, which had two humps instead of Toblerone's single peaks, after receiving a legal warning from Mondelēz. The bar was eventually relaunched after Poundland changed the colour of the packaging and the shape of the bar, and it remains on sale.