Sainsbury’s and Asda are seeking a judicial review for a delay in the Competition and Markets Authority’s (CMA) inquiry into their proposed £7.3bn merger.

The supermarket groups claim that the current timetable does not give them, or the CMA, “sufficient time to provide and consider all the evidence given the unprecedented scale and complexity of the case”.

Sainsbury’s, which announced its plans for a merger with Asda in April this year, said in a statement: “Both parties have engaged constructively with the CMA to date and have made repeated requests for additional time.

“Specifically, we have asked the CMA for an additional 11 working days over the Christmas period to respond to a large amount of material recently provided to us.

“We are confident in the merits of the deal and our ability to deliver the synergies. By bringing our two businesses together, we will invest further in range, quality and customer service, while lowering prices and reducing the cost of living for millions of UK households.”

The CMA launched its in-depth, phase two investigation into the proposed merger in September, led by an inquiry group chosen from its independent panel members. The CMA said its main priority was assessing whether shoppers would face higher prices or lower quality of service as a result of the merger and, if so, to prevent that from happening.

“Investigating any merger of this size requires assessing a large volume of material in a short timeframe, and it is not unusual for the companies involved to do this,” it said in response to today’s (Wednesday) request.

“We have done everything we can to aid their consideration of this work, whilst still ensuring we are able to meet our legally-binding deadline. This includes extending certain administration timelines where appropriate.

“If we gave the companies the extra time they are now asking for, it would put our ability to complete the investigation by the required deadline at very serious risk.”