The Competition and Markets Authority (CMA) has formally opened its investigation into the proposed Sainsbury’s-Asda merger.

The first phase of the investigation runs until June 4. During this period, the CMA will explore whether the deal ”could reduce competition and choice for shoppers”.

Only in the next phase of the investigation, after the pre-notification stage, will the authority be able to identify whether there is a ’substantial lessening of competition’ as a result of the proposed merger.

Sainsbury’s and Asda announced plans to merge their two businesses last month. The merger would see more than 2,800 Sainsbury’s, Asda and Argos stores - and several of the UK’s most-visited retail websites - trade under one combined business.

CMA director of mergers Colin Raftery will be responsible for the day-to-day running of the investigation into the proposed merger, including having an advisory role to the decision-makers.

The CMA is now seeking views on the merger from all interested parties. Further details will be available on the investigation case page.