The Competition and Markets Authority has launched a formal inquiry into the £780m merger of Marston’s and Carlsberg’s brewing operations.

The companies agreed a deal in May to merge Marston’s brewing arm with Carlsberg’s UK division and create new a joint venture.

The CMA has now launched a ‘phase 1’ investigation following the European Commission’s decision to refer the case to the United Kingdom, and invited comments.

The competitions regulator will consider whether the deal could lead to “a substantial lessening of competition within any market or markets in the United Kingdom for goods or services”.

The invitation to comment is open until 2 September, with the deadline for the phase 1 decision and whether to launch a more in-depth ‘phase 2’ investigation by 19 October.

The proposed merger will see Marston’s take a 40% stake in the newly created Carlsberg Marston’s Brewing Company as well as a cash payment of up to £273m.

Marston’s previously stated: “We do not expect that the transaction raises any competition concerns and are satisfied that the group has sufficient liquidity in place to meet its requirements ahead of completion.”

CAMRA (the Campaign for Real Ale) warned of its “serious concerns” the JV, including “market foreclosure for small brewers, which will reduce choice for beer drinkers and pub-goers”.