Shares in Spanish telco giant Telefonica were trading 4% higher at 4.35 Euros ($4.76) Monday after it confirmed that it is in talks with John Malone’s cable company Liberty Global about the merger of its U.K. mobile-phone operator O2 with Liberty Global’s Virgin Media, a leading provider of pay-TV, broadband, fixed-line and cell-phone services to British customers.

The merged company would be worth $30 billion, according to Goldman Sachs, and control a market-leading 34% of the U.K. telecoms market, by revenue. This would threaten the position of current market leader BT, which has a 32% slice of the market. It would also deliver synergies as the companies would be able to make savings by combining back-office operations and infrastructure, which Deutsche Bank said could total £6 billion ($7.45 billion).

In a statement, Telefonica said: “The process initiated by both parties is in a negotiation phase, not being able to guarantee, to this date, neither the precise terms nor the probability of its success.”

Virgin Media had 6 million TV and broadband, and 3.3 million mobile subscribers at the start of this year, with revenue totaling $6.6 billion last year.

Telefonica UK, which includes the O2 mobile business, had 34.5 million customers at the end of 2019, with revenue of 7.1 billion Euros ($7.8 billion) last year.