Tesco's acquisition of a former Co-operative Group store in Slough, Berkshire, has reduced competition and choice in the area, the Competition Commission has provisionally concluded.

The store is the subject of a parallel investigation to the Competition Commission's main groceries inquiry and could prove to be the first test case for the commission's new local market definition.

Tesco's acquisition of the store in 2003 “has resulted in a substantial lessening of competition in the market for grocery retailing in Slough”, the commission said.

“We have provisionally concluded that Tesco's acquisition of this store has led to a significantly less competitive situation than if it had been bought by a rival retailer,” said inquiry group and commission chairman Peter Freeman.

“The two stores had an overlapping catchment area and although there are other large stores in the area, the extent to which they can compete with Tesco's Brunel Way store is limited by other factors.”

The commission will now examine potential measures to address the loss of competition. It has already ordered Tesco to stop building a new store on the site.