(Close): BT shares climbed 2.2% after the owners of the EE mobile phone network confirmed they were in talks over selling EE to the UK firm.
On Monday, BT said it was in talks with two mobile operators about a possible purchase, with one network being Telefonica's O2.
Deutsche Telekom and Orange, joint owners of EE, have now confirmed that EE is the other firm being eyed by BT.
The benchmark FTSE 100 index closed almost flat, down 2 points at 6,729.17.
But the biggest downward move came in the FTSE 250, where shares in Thomas Cook sank more than 17% after its chief executive quit.
Harriet Green - who joined the travel firm two years ago - stunned the markets with her resignation. She said her work at the company was "complete".
Ms Green will be replaced by chief operating officer Peter Fankhauser, who will take over with immediate effect.
Shares in rival travel company Tui fell 2%.
Catering group Compass fell 1.3% despite the company reporting a 5.4% rise in underlying pre-tax profits to £1.16bn.