Waitrose is battling allegations of chocolate plagiarism in a hot-tempered dispute between rival factions of posh chocolatiers.

The bosses of upmarket Hotel Chocolat have written to the supermarket’s chief executive in fury after it launched a range of bars they claim bear an uncanny resemblance to their own.

The firm has won backing from fellow independent chocolatier Choc on Choc, which believes Waitrose’s avocado Easter egg is suspiciously similar to one of its own inventions.

Hotel Chocolat’s co-founder Angus Thirlwell said eagle-eyed chocoholics first spotted the alleged copycat bars in Waitrose earlier this week and alerted him to the similarity.

“I’m peeling myself off the wall in terms of emotion because it’s one of the first products I designed,” Thirlwell said.

“They’re running adverts like it’s some amazing piece of creativity and you just think: ‘Hang on, this is a complete rip-off.’ It’s got to stop.”

“We’re hoping that they’ll do the right thing,” he said but also warned that Hotel Chocolat has not ruled out legal action.

“Look at how [engineer James] Dyson has had to fight to protect his ideas over and over again,” he added. “We’re determined to defend our brand.”

All the Waitrose bars are roughly the same size as Hotel Chocolat’s and share a distinctive wavy edge that sets them apart from mass-produced bars with straight sides.

One of the Waitrose bars – made of white chocolate with studs of meringue and strawberry pieces and named Eton mess after the famous pudding – is a combination almost identical to Hotel Chocolat’s concoction of the same name.

Waitrose’s caramel crunch bar also shares several characteristics with Hotel Chocolat’s Caramel & Co offering, while orange and coffee-flavoured iterations echo products that the chocolatier has discontinued.

Thirlwell said Hotel Chocolat had legal protection for its its curved-edge design from the European Union’s intellectual property office.

“It’s inspired by what happens when you pour molten chocolate out onto a chocolatier’s marble table-top because it spreads into a lovely curvy outline,” he said.

Thirlwell initially highlighted the uncanny similarities on Twitter. There he found support from Choc on Choc, which said it had invented a chocolate avocado in 2015, only to see Waitrose subsequently roll out a similar avocado egg for Easter.

“We’re coming up with these great concepts but we’re not asked to manufacture them for them [supermarkets]. What happens is that people take the ideas and use them,” the co-founder Flo Broughton said.

“When a larger retailer copies it or does something very similar, people think that we’ve copied them.

“We didn’t raise our concerns at the time because we’re a supplier to Waitrose and I was too chicken.”

A spokesperson for Waitrose said: “We take the intellectual property rights of other businesses extremely seriously and so we are looking into the points made by Mr Thirlwell.

“However, we were only approached about this matter yesterday afternoon and we will, of course, need to consider the issues raised, which we will urgently.”

Thirlwell said there was no comparison between the two products in terms of quality because Hotel Chocolat bars have a much higher cocoa content, whereas the main ingredient in most of the Waitrose bars is sugar.

“It’s one thing ripping off the look but it’s another when they’ve been stuffed full of cheap sugar. There’s a difference in taste quality and that’s because sugar is one tenth the price of cocoa,” he said.

The dispute marks the second time within months that the chocolate world has been hit by allegations of plagiarism.

Poundland and the US confectionery giant Mondelēz ended up in court over allegations that Poundland’s Twin Peaks bar was a rip-off of Toblerone but with two points instead of one.

The two sides eventually reached a settlement that allowed Poundland to sell half a million Twin Peaks bars it had already produced, in exchange for changing the shape, which it claimed was inspired by Wrekin and Ercall hills in Shropshire.