The UK's competition watchdog is concerned that the proposed deal would lead to higher prices for millions of mobile phone users across the country.

The report from the CMA explains: "The investigation, led by an independent inquiry group, has provisionally concluded that the merger would lead to price increases for tens of millions of mobile customers, or see customers get a reduced service such as smaller data packages in their contracts.

"The CMA has particular concerns that higher bills or reduced services would negatively affect those customers least able to afford mobile services as well as those who might have to pay more for improvements in network quality they do not value."

The industry watchdog noted that there are some potential benefits to the proposed merger.

However, the CMA suggested that these benefits have been "overstated" by the companies.

The report explained: "While identifying these concerns, the CMA has also found that the merger, by integrating the Vodafone and Three networks, could improve the quality of mobile networks and bring forward the deployment of next generation 5G networks and services, as claimed by Vodafone and Three.

"But the CMA currently considers that these claims are overstated, and that the merged firm would not necessarily have the incentive to follow through on its proposed investment programme after the merger."