Marks & Spencer has started legal action against Aldi in a bid to protect its Colin the Caterpillar cake.
Aldi has produced a Cuthbert the Caterpillar cake and M&S are arguing that the product infringes its trademark.
M&S, which lodged an intellectual property claim with the High Court this week, say that the similarity of Aldi's product leads customers to believe it is of the same standard and "ride on the coat-tails" of M&S's reputation with the product.
M&S wants Aldi to remove the product from sale and agree not to sell anything similar in the future.
M&S launched Colin the Caterpillar around 30 years ago and his appearance has been substantially unchanged since around 2004, except for adaptations for events such as Halloween and Christmas, and related products such as Connie the Caterpillar.
The product is central to M&S's partnership with cancer charity Macmillan, and the retailer has created a Colin product for the annual World's Biggest Coffee Morning fundraising event.
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The cake is a sponge with milk chocolate and buttercream, topped with chocolate sweets and a smiling white chocolate face.
M&S has three trademarks relating to Colin, which the retailer believes means Colin has acquired and retains an enhanced distinctive character and reputation.
A spokesman said: "Because we know the M&S brand is special to our customers and they expect only the very best from us, love and care goes into every M&S product on our shelves.
"So we want to protect Colin, Connie and our reputation for freshness, quality, innovation and value."