BT has been cleared to buy mobile phone operator EE in a tie-up worth £12.5 billion.
The Competition and Markets Authority has ruled that the merger "was not expected to result in a substantial lessening of competition in any market in the UK".
The decision is likely to draw ire from rival telecoms companies as it creates the biggest company across broadband, fixed line and mobile.
But the CMA said even if BT attempted to use its dominance in back haul companies used to carry mobile traffic, it would not create a monopoly across the industry.
It also decided that the merger would not reduce competition as much as if the two companies had both been mobile companies - even though it is a significant tie up of a broadband and a mobile company.
BT's Chief Executive Gavin Patterson said the combined BT and EE deal: "would be good for the UK, providing investment and ensuring consumers and businesses can benefit from further innovation in a highly competitive market".
Additional reporting by Reuters.
