The Office of Fair Trading has sounded a note of caution over the proposed merger between Orange and T-Mobile. The agency says that the deal "threatens significantly to affect competition in mobile telecommunications in the UK".

The OFT has asked the European Commission if it can take a deeper look at the impacts of the merger on the UK market. The deal would create a massive phone operator with more than 28 million customers. It's worried that this would reduce the choice that customers have, and cause prices to rise.

If the concerns are still present when the investigation has been completed, the matter can be referred to the Competition Commission, who has the power to block such a merger from taking place. The two companies have both signed the final agreement for their UK operations to be combined.