Tesco’s acquisition of the Mills Group via its wholly owned subsidiary One Stop stores has been rubber-stamped by the Office of Fair Trading (OFT) despite the protests of small store groups.

The purchase of the north east-based convenience store chain will boost the group’s portfolio by 76 stores – one less than originally planned. Tesco-owned One Stop announced the acquisition for an undisclosed fee in December, prompting the OFT to "invite comment" on the takeover.

The Association of Convenience Stores (ACS) said it was furious that the OFT had failed to understand the “implications of the persistent growth of Tesco’s ‘shadow brand,” and block the acquisition.

ACS chief executive James Lowman said: “If Tesco sought to takeover a company operating 76 large supermarkets then it would most likely be blocked. We fail to see any reason why this merger has been treated differently.

“The OFT has once again failed to fully consider the implications of this for choice and competitiveness in the long term."

A spokesman for the OFT said the merger was “too small to make a difference at a national level.”

The acquisition will bring the number of One Stop stores to 598 across England and Wales. Mills Group chief executive officer Nigel Mills has retained nine stores.