Representatives from Vodafone and Three have told MPs their planned merger will not increase prices, despite it reducing the number of competitors in the mobile market.

The firms plan to merge their UK-based operations, creating the biggest mobile network in the UK with around 27 million customers.

The deal still needs to be approved by regulators.

But the Unite union says bills could rise by £300 per year if it goes ahead.

The UK currently has four major mobile operators - Vodafone, Three, EE (which is part of BT), and Virgin Media O2.

Speaking to the Business and Trade Committee on Tuesday, Unite's investigative researcher George Stevenson said combining Vodafone and Three would be bad for consumers.

"The UK is perfectly capable of supporting four or many other mobile network operators," he said.

"But if we have this merger take place, we're going to see price rises, we're going to see profits go up."

But Three general counsel Stephen Lerner said there were "no merger related price rises" in the firms' joint business plan.

"I want to make it clear: it's not part of the transaction rationale, and we are not planning any increases in prices," he said.

The firms said they were in talks with the Competition and Markets Authority (CMA), which will review the potential impact of the merger.

Mr Lerner said he was "confident" the CMA would approve the merger, which the firms say will lead to £6bn of investment in its first five years, and £11bn in total.