A new merger between Vodafone and Three looks set to create the UK’s biggest mobile network, surpassing Virgin Media O2.

The deal must still be approved by regulators who will consider issues including whether the move would push up consumer prices.

The Competition and Markets Authority (CMA) said that, with millions of consumers and many businesses relying on the services of Vodafone and Three, it was only right that it should review the possible impact of a merger on competition.

The two companies said customers would be given a better network experience with more coverage and greater reliability at no extra cost “from day one”.

They also said they would invest £11bn into 5G technology in the UK over the next decade.

Vodafone and Three are currently the third and fourth largest mobile providers in the UK, respectively.

Virgin Media O2 is currently the market leader with around 24 million mobile users, and the BT Group-owned EE has around 20 million mobile customers.

If the Vodafone-Three merger goes ahead, it would combine the two companies’ UK operations with around 27 million customers – taking the new entity ahead of both Virgin Media O2 and EE.

Vodafone would own 51% of the newly merged business, with CK Hutchison – the owner of Three UK – controlling the rest.

Consumer group Which? said reducing choice in the number of major mobile providers risked raising prices. Still, Karen Egan, head of mobile at research firm Enders Analysis, said this had yet to prove the case for similar deals in other countries.