LONDON, DEC. 23 -- Britain's Panel on Takeovers and Mergers today gave British Petroleum Co. permission to go ahead with its $2.9 billion bid for Britoil PLC, but the British Treasury continued to vow to use its "golden share" powers to block any bidder from gaining control of the country's largest independent oil company.

Britoil, target of a $4.1 billion takeover bid by British Petroleum Co. PLC, has reached a friendly agreement under which Los Angeles-based Atlantic Richfield Co. will acquire a partial stake in the company.

However, the "golden share" provision allows the government to outvote all other shareholders at a general meeting on any resolution if a bidder gains control of more than 50 percent of Britoil's shares.

The government retained a golden share in Britoil when it privatized the company in two stages in 1982 and 1985.

Today's announcement restated the Treasury's position, first made public on Friday. Earlier today, the government's Panel on Takeovers and Mergers approved BP's full takeover offer.

The panel, an independent regulatory body, said that blocking BP's offer for Britoil, a Scottish-based North Sea oil exploration company, would deprive Britoil's "ordinary shareholders of the opportunity to consider the BP offer on its merits."

BP said it would seek talks with government officials and Britoil board members. BP has left open the possibility of acquiring ownership, but not control, of Britoil.

Meanwhile, Atlantic Richfield spokesman Scott Loll said in Los Angeles today that Arco had increased its stake in Britoil to 20.4 percent, or about 100 million shares.

Arco previously reached an agreement to acquire a 49.9 percent stake in Britoil, the first 29.9 percent through purchases on the open market at $6.30 a share, and the rest through the swap of Arco assets for new Britoil shares. It has said it would consider making a full bid for Britoil if BP did.

Loll said Arco's executives in London were flying back to the United States today to confer with corporate officials, and that the company would have no further comment regarding the panel's decision favoring BP's bid.

"We are evaluating our options," Loll said.