The UK’s Competition and Markets Authority (CMA) has initiated a probe into the proposed joint venture (JV) between brewers Carlsberg and Marston’s to find whether the deal would stifle competition in the market.

In May, the two firms announced their JV plans to reduce costs.

The Carlsberg Marston’s Brewing Company JV will have control of Carlsberg UK’s London Fields and Northampton breweries, as well as its national distribution centre.

In addition to 11 distribution depots, Marston’s six breweries – Marston’s, Wychwood, Jennings, Banks’s, Eagle and Ringwood – will come under the JV.

This £780m ($1bn) deal was expected to close in September.

Now with the CMA’s probe, the closure deadline has been extended by four weeks.

Carlsberg is the majority shareholder in the JV with a 60% stake while Marston’s will own the remaining stake.

This deal will take the value of Marston’s brewing business by up to £580m ($765m), while Carlsberg’s to £200m ($263m).

Following the completion of the deal, Marston’s will receive £273m ($360m).

Members of the brewing industry can submit comments on the deal to the CMA until 2 September.

The deal was opposed by Campaign for Real Ale (CAMRA), which lobbied for a CMA probe in July.

CAMRA chief executive Tom Stainer said: “CAMRA is pleased that the Competition and Markets Authority has listened to our calls and opened an initial investigation into the proposed Carlsberg Marston’s Brewing Company.

We will now be asking the CMA to move to a full investigation, given our serious concerns about anti-competitive effects of the JV, including market foreclosure for small brewers, which will reduce choice for beer drinkers and pub-goers.

This is why the CMA must make sure that any merger does not stifle fair competition, access to market for brewers, and ensure decent consumer choice of beer in pubs up and down the country.”