(Sharecast News) - Vodafone and Three UK have been told to find ways to assuage Britain's competition regulator that their planned $19bn merger would not leave consumers worse off or face a full investigation.

The Competition and Markets Authority (CMA) gave the duo five working days to provide "meaningful" solutions to concerns that the merger of the two UK operations would lead to higher prices for customers and lower investment.

Britain has four mobile telecoms networks: EE, Three, Virgin Media/O2 and Vodafone.

"Whilst Vodafone and Three have made a number of claims about how their deal is good for competition and investment, the CMA has not seen sufficient evidence to date to back these claims," the CMA said on Friday.

"These warrant an in-depth investigation unless Vodafone and Three can come forward with solutions."

Reporting by Frank Prenesti for Sharecast.com