LONDON Executives from Vodafone and CK Hutchison's Three UK unit said their 15 billion pound ($18 billion) merger would benefit Britain's consumers, infrastructure and jobs, as lawmakers scrutinise the planned tie-up.

Vodafone and Three UK have pledged to invest 11 billion pounds to build a 5G network for Britain as part of their bid to secure backing from politicians, unions and competition authorities for the merger announced in June.

Britain's antitrust watchdog last week kicked off its examination of the deal, while lawmakers from the business and trade committee on Tuesday asked what the deal would mean for jobs.

"We believe that actually jobs will be created as a consequence of this merger both for building the network, and to create and support the IT systems, and to maintain this new network," Vodafone UK's corporate affairs and sustainability director Nicki Lyons said.

She said the companies were not giving numbers at this stage, and conceded that head office duplication could be an issue.

Trade union Unite has warned the deal will result in higher bills and job losses.

Representatives from both the companies said that as the current No. 3 and No. 4 players in Britain's mobile market they did not have the scale to invest and compete against the two biggest operators, BT's EE and VM O2, jointly owned by Telefonica and Liberty Global.

They warned that without the deal, Britain's 5G network would continue to lag that of other European nations.

"Neither us nor Vodafone can invest sufficiently to build the type of 5G network that's needed," Three's Chief Technical Officer David Hennessy said.

The two companies have long known that a proposed merger would face intense scrutiny from regulators who have previously opposed deals that reduce the number of networks in major markets from four to three.

But the tie-up would not result in price rises for consumers, said Three's general counsel Stephen Lerner.

"We are not planning any increases in price," he said, explaining the merged entity would be keen to price competitively to ensure it filled the new capacity it wants to build.

($1 = 0.8223 pounds)

(Reporting by Sarah Young; Editing by Mark Potter)