John Lewis has branded the Office of Fair Trading "mad" after it left the high street store out of a website comparing the price of extended warranties.
As the department store doesn't charge extra for extended warranties and includes them in the total price, the OFT said it shouldn't be included.
In response the shop's managing director blasted the regulator for the "irrational" behaviour.
The new website from the OFT, which is set to be launched later this month, has been designed to help shoppers make like-for-like comparisons of extended warranties. The site was due to be launched last year, but was delayed because of development issues.
It includes all the major retailers, such as Argos, Dixons and Currys, so shoppers can compare prices and services before buying a product.
But as John Lewis doesn't conform to the same pricing structure, it has been left out, causing an angry backlash from the retailer.
Andy Street, managing director for John Lewis, told the Daily Telegraph: "The OFT is supposed to exist to defend consumer interest. This is a clear case where it is acting in exactly the opposite way.
The retailer even tried to overturn the decision in March but the competition appeals tribunal agreed with the OFT.
In response Russell Guthrie, spokesperson for the OFT, explained that as John Lewis's "inclusive" product is different from that offered by most other providers, a meaningful comparison is not possible.
"The website clearly and prominently states that so called inclusive warranties are available, so consumers are aware of this option.
"We would also very much welcome it if John Lewis wanted to join the site for its standalone extended warranty products, something we have repeatedly emphasised to John Lewis," he said.
When buying a new product, such as a TV or a washing machine, an extended warranty can provide some protection should something go wrong. They cover the price of repairs or replacement and most run for between three to five years.
But one of the main problems with these policies is how they are sold. As the majority are bought at the point of sale, aggressive sales tactics are often used which can mean you are pressured into paying over the odds and not shopping around.
Many experts also believe these policies are a rip-off as customers already have protection under the Sale of Goods Act 1979 and the manufacturer's warranty.
You can read more in our article Why extended warranties can be an expensive mistake.
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