Altice UK has increased its stake in BT Group, the leading telecom operator, from 12.1 percent to 18 percent.

BT Group said the management will continue to operate the business in the interest of all shareholders and remains focussed on the successful execution of its strategy and building on recent performance momentum.

Altice also controls SFR, the second largest telecoms operator in France behind Orange. Patrick Drahi is the founder of Altice.

Britain warned it would intervene if necessary to protect the telecoms group building the country’s critical fibre network.

“The government is committed to levelling up the country through digital infrastructure, and will not hesitate to act if required to protect our critical national telecoms infrastructure,” a spokesperson said.

Altice increased the stake, at a price of 1.02 billion pounds based on BT’s closing share price on Monday, after a previous six-months’ standstill expired at the end of last week, media reports indicated.

Patrick Drahi, BT’ biggest shareholder who has pursued debt-fuelled deals to buy assets in France, the United States, Portugal and Israel, said he did not intend to make a full bid for the 16.6 billion pound ($21.9 billion) company.

The Franco-Israeli entrepreneur, who bought 12.1 percent of BT in June, said he engaged constructively with BT’s board and looked forward to continuing that dialogue.

Patrick Drahi notified BT’s new chairman Adam Crozier on Monday after the market had closed. BT boss Philip Jansen and Crozier met Digital Secretary Nadine Dorries earlier on Monday.

BT’s second largest shareholder is Deutsche Telekom. The German company’s boss Tim Hoettges said in September it was weighing options for its 12 percent stake and expected some kind of movement in the next 12 months.