Hong Kong's CK Hutchison and Vodafone have unveiled the long-awaited 15 billion pound (US$19 billion) merger of their British mobile operations on Wednesday, saying the creation of a new market leader would help drive competition and investment.

Expected since the two companies disclosed talks in October, the deal faces prolonged scrutiny by the anti-trust regulator into whether having a single operator with 27 million customers could lead to higher mobile prices.

Seeking to win over politicians, unions and the competition authorities, the two groups said they would invest 11 billion pounds to create "one of Europe's most advanced standalone 5G networks".

Vodafone's new CEO Margherita Della Valle said the deal was a "game changer" in its home market, and that it was good news for customers, the country and competition.

Vodafone will own 51 percent and Hutchison 49 percent of the combined group, which will be led by current Vodafone UK boss Ahmed Essam. The finance chief of Hutchison's Three UK, Darren Purkis, will take the same role in the new group.

The combined operator will overtake BT's EE and VM O2, jointly owned by Telefonica and Liberty Global .

Vodafone, Britain's third-biggest mobile operator, will have an option to buy-out the Hong Kong-based conglomerate three years after completion, if it agrees.

The deal will face intense scrutiny from regulators who have previously opposed deals that reduce the number of networks in major markets from four to three. Hutchison's attempt to merge with Telefonica's O2 in Britain seven years ago was blocked.

The companies said the transaction would need approval under a UK National Security and Investment Act, which gives the government powers to intervene in deals that could pose a risk.

They will present their plans to Britain's Competition and Markets Authority (CMA) in the coming weeks.

"We believe that this case stands on very strong grounds," Vodafone's Essam told reporters, adding that customers would be getting a much better network for the same price. "We're very confident on our case."

Hutchison's Three UK boss Robert Finnegan pointed out that the planned investment was substantially higher than rivals', and said while a rejection by the CMA would not lead to Hutchison exiting Britain, it would have to reduce investment. (Reuters)