A proposed merger between food delivery service Just Eat and rival Hungryhouse has been referred to the Competition and Markets Authority (CMA).
The probe, which will run until November this year, comes amid fears that the tie-up between the two companies could result in worse terms for restaurants.
Earlier this month, Just Eat said it was "committed to demonstrating to the CMA that the market is, and will remain, competitive following completion of the proposed transaction".
The home delivery sector, which also features firms such as UberEats and Deliveroo, has become increasingly competitive.
At the ALMR spring conference earlier this month, John Upton, managing director of fast casual chain Leon, noted that orders of food for delivery at the business had leapt from £15,000 a week to £70,000 a week as consumer habits changed.
Just Eat, which was founded in Denmark in 2001, announced it was acquiring Hungryhouse in December last year. The company also announced the acquisition of Canadian firm Skipthedishes for £66m, which features 2,900 restaurants, to expand its operations in the country.
Just Eat said that the Hungryhouse integration would be generate additional EBITDA of £12-15m, excluding integration costs of £1m.
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