LONDON — The planned merger of T-Mobile UK and Orange warning has created doubt of the Office of fair trading which could be a threaten competition.

"The OFT's initial view, following consultation, is that the joint venture threatens significantly to affect competition in mobile telecommunications in the UK," the agency said in a statement.

T-Mobile UK, which is owned by Germany's Deutsche Telekom, and Orange, which is owned by France Telecom, is planning to join forces too create a mobile operator that would have a 37-percent market share in Britain, beating nearest rival Vodafone - which holds 25 percent of the market.

The watchdog said it had made a formal request to the European Commission, which is also looking into the proposed merger, to refer the British aspects of the deal back to the OFT.

If the request is granted, the OFT said it would then examine the merger proposal to see if it required a more "in-depth investigation."