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The deal boosts the number of TalkTalk's residential broadband subscribers to around 4.25 million - about a quarter of the UK market.
The commission concluded that the transaction "would not significantly impede effective competition" in the European Economic Area, or any substantial part of it.
Carphone Warehouse is the UK's largest independent retailer of mobile handsets and connections and a range of associated devices, such as laptops. It has also increasingly moved into providing communications services such as broadband and dial-up internet access as well as fixed-line and mobile telecommunication services.
Tiscali UK provides telecommunications and internet services, supplying broadband and narrowband internet access services, fixed-line telecommunication services and digital TV services to business and domestic customers.
The commission said their activities overlapped horizontally in supplying retail and wholesale internet access, as well as in retail fixed-line telephony. It said the merged company would become one of the main competitors to the incumbent operator BT, but would also face competition from cable operators like Virgin Media, and other mobile network operators.