Tesco has slammed a proposal by the Competition Commission to appoint a regulator to enforce a new, tougher code of conduct.

In its provisional findings, commission chairman Peter Freeman said he believed the code "was effective in terms of supermarket behaviour. The idea it wasn't is wrong. The trouble is, it's rather flexible."

The commission concluded that the code needed tightening after uncovering "one or two instances of unconscionable behaviour" among thousands of emails sent between Tesco and Asda and their suppliers that it examined this summer.

Among the 'possible remedies' proposed in the provisional findings were the inclusion of more retailers and better monitoring, perhaps through an ombudsman.

The commission said it had found evidence that retailers were transferring 'unexpected costs and risks' to suppliers and making retrospective changes to agreements. It was worried such practices could lead to suppliers becoming reluctant to innovate, which would limit consumer choice.

But Tesco said it feared the appointment of a regulator to remedy this could have "perverse outcomes". "If the ombudsman got involved in how much we pay for goods, it may be we cannot pass on the good deals to our customers," said a spokeswoman.

"When an ombudsman has been introduced to other industries it's been to protect the consumer interest. This one seems to be about protecting the producer's interests."

Any move to ban retrospective changes would potentially damage competition, she added, as it would restrict retailers' ability to respond to the market.

Although the commission said some trading practices could undermine innovation, this was disputed by one branded supplier. "Real innovation comes from suppliers and is initially supported by retailers to see if a concept has legs," she said. "The minute it is successful, retailers bring out a cheaper own label version."