Shares in BT were among the best gainers on a neutral FTSE 100 on Tuesday, as investors warmed to speculation surrounding its potential return to the mobile telecoms market. A report in Spain’s El Confidencial newspaper said the UK company was considering offering €6bn on top of taking a 20 percent stake in the Spanish company to buy its British operations, O2, which BT used to own. The two companies confirmed they were in talks about a potential deal on Monday, without giving details. BT rose 1.6 percent to 400.2p.