The Competition and Markets Authority (CMA) has been looking into the deal to protect customers from price rises to their mobile tariffs and to make sure competition in the telecoms market is not reduced.
We take a look at what the tie-up between the UK's third- and fourth-biggest mobile network operators could mean for consumers.
Why do Vodafone and Three want to merge their UK operations?
The companies argue that the merger, which would create the UK's largest retail mobile operator by revenue, and the second largest in terms of customers, with some 27 million subscribers, is needed to compete and drive investment to achieve the government's goal of nationwide access to 5G by 2030.
The market value of Vodafone, which is making the largest round of job cuts in the telecoms group's history, has slumped more than 70% over the past decade. Three UK, owned by CK Hutchison, has said costs have doubled over the past five years, meaning it now cannot sustain the level of investment in its mobile network.
The companies argue the combination of the two companies will give it the scale needed to compete against the "big two", the EE owner, BT, and Virgin Media O2, including on the rollout of 5G and competitive pricing.
However, the CMA has previously expressed concern that the tie-up could result in a "substantial lessening of competition" in the UK's retail and wholesale markets, and could lead to price rises for tens of millions of mobile customers.
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