Tim Steiner has launched a verbal broadside at Ocado’s competitors amid mounting speculation over the online specialist’s growth prospects.

Responding to suggestions that rivals were growing online sales faster than Ocado, Steiner told The Times: “The only person who claims to be growing faster is Sainsbury’s but they have not put out audited numbers. Until they do, I reserve my right to believe or not believe what they say.”

“It’s not new growth to them. It’s the same customer shopping in a different way. It’s cannibalising the bricks-and-mortar business. I’m not sure why they are bragging at all.”

His comments came after Ocado reported sales growth of 12% for the past six months, while profits were almost flat at just £181,000.

Steiner admitted to investors that Ocado had missed out on a Jubilee bonanza to bricks-and-mortar retailers, pointing instead to “disruption” from the celebratory weekend. He also warned of “uncertainty” in third-quarter trading due to the Olympic Games, which are widely expected to provide a fillip to conventional retailers.

Shares in Ocado plummeted by 20% in trading yesterday as a result of the cautious outlook.

Steiner told The Times Waitrose was still a “minor operator” online had achieved much of its recent growth through heavy discounting.

“If you give groceries away, there are customers that will take them from you. The percentage of that growth that’s in heavily discounted incentives is massive. They’re still a minor operator and they’re not our competition. Tesco and Sainsbury’s are our competition.”