Mobile termination rates have already fallen drastically, down 80 percent since 2011 from about 4 pence a minute to 0.8 pence. A decade ago, termination rates, which apply to calls from landlines as well as mobiles, were about 14 pence a minute.

Ofcom said a new mobile charge control, applying to all operators, would see rates fall slightly further, to less than half a penny per minute by April 2017 in real terms.

Ofcom Competition Policy Director Brian Potterill said consumers were benefiting from a thriving competitive market.

"The average cost of a call bundle has fallen from 40 pounds to around 13 pounds in real terms over the last ten years," he said.

"We want to ensure mobile users continue to benefit from competition, which will deliver affordable services in the years ahead."

Britain has four major network operators: EE, a joint venture between Deutsche Telekom (>> Deutsche Telekom AG) and Orange (>> ORANGE SA), Vodafone (>> Vodafone Group plc), Telfonica's (>> Telefonica SA) O2 and Hutchison's (>> Hutchison Telecommunications HK Hld Ltd) Three.

Ofcom said it expected to publish its final decisions by March 2015.

(Reporting by Paul Sandle; Editing by Neil Maidment)