BT's £12.5bn takeover of mobile phone network EE has been approved by The Competition and Markets Authority (CMA).
The deal means BT, the largest fixed-line phone business in the UK, will take control of the UK's largest mobile phone operator, EE.
Last October, the CMA gave provisional clearance to the deal, which has faced a backlash from competitors such as Vodafone who say it concentrates market power.
Now the competition watchdog has granted final approval to the merger, saying it "is not expected to result in a substantial lessening of competition in any market or markets in the UK."
The decision was mainly based upon BT's strength in the fixed-line market and EE's strength in the mobile market which, the CMA says, means competition in both markets is unlikely to be affected by the deal.
BT will add EE’s 24.5 million direct mobile subscribers to the 10 million existing customers it already has, making it the largest telecoms provider in the UK.
John Wotton of the CMA said: "Since our provisional findings, we have taken extra time to consider responses in detail but the evidence does not show that this merger is likely to cause significant harm to competition or the interests of consumers.
"As BT is a smaller operator in mobile, it is unlikely that the merger will have a significant effect.
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"Similarly, EE is only a minor player in retail broadband, so again it is unlikely that the merger will have a significant effect in this market."
The acquisition was originally announced in February last year, promting rivals TalkTalk and Vodafone to call for an independent Openreach.
BT's Openreach division supplies services to rivals in the telecoms sector, allowing them access to the UK's copper and fibre communications cable network.
Addressing the concerns, Mr Wotten said: "We have heard wider concerns about the sector, including about Openreach and its regulation by Ofcom.
"Our job has been to examine the specific impact of this merger on competition and consumers and, where relevant, we’ve looked at how these issues might be affected by the merger."