British telecom giant BT could offer almost £5bn to Spanish firm Telefonica to purchase O2 mobile network.On Tuesday, Spanish newspaper El Confidencial reported BT could offer at least €6bn (£4.76bn) on top of a 20% stake in its share capital for the company it originally spun off in 2001.Including the €6bn, the deal's total value would be around €14bn, significantly less than the €22.7bn Telefonica paid to purchase O2 in 2005. The Spanish firm has said that O2 remains core to its business but refused to rule out the possibility of selling the mobile network, as it aims to bring debt below €43bn by the end of 2014.At 10:35 on Tuesday BT shares were up 1.67% to 400.7p, while Telefonica shares were up 1.07% to €12.73.