A probe is being demanded after a Tesco-owned chain of convenience stores based in the West Midlands took over a rival firm.

Brownhills-based One Stop announced on Thursday it had bought 77 small stores in the North East, Cumbria and Yorkshire from Mills Group.

But the Association of Convenience Stores (ACS), which represents 33,500 corner shops and convenience stores, has called for an investigation into the growth of One Stop.

It argues that One Stop, which is owned by Tesco, is a shadow brand of Tesco.

ACS’s chief executive, James Lowman, said: “The competition authorities have repeatedly failed to grasp the implications of the continuing growth of Tesco’s shadow brand.”

A Tesco spokesman said One Stop, which is based in Apex Road, was run separately as a different business.