BG Group, the British oil and gas giant, went hostile yesterday with an ambitious all-cash A$13.8 billion (£6.7 billion) offer for the Australian energy group Origin Energy, pitched directly to shareholders.

BG has offered A$15.50 a share - the same price that the board of Origin rejected less than a month ago when talks between the two energy groups broke down at the eleventh hour. The British company sees Origin as a route to increasing its presence in the expanding Asia-Pacific region and bolstering its assets in coal-seam gas (CSG) - methane gas trapped underground by water in deep coal seams.

BG said that it saw the takeover as part of creating a global “integrated energy model - creating value from reservoir right through to burner tip”.

The all-cash bid represents a 48 per cent premium on Origin's share price of A$10.47 immediately before the first bid was launched. Announcing the bid in Sydney yesterday, Frank Chapman, the BG chief executive, said that Origin had been wrong to reject the same offer and he was confident that a direct appeal to shareholders would prove attractive.

The management of Origin pulled out of the BG deal last month after Santos, an Australian rival, secured an A$2.5 billion investment from Petronas, the Malaysian energy group, for another significant CSG project. Origin claimed at the time that, based on that deal, its CSG reserves alone were worth A$16 billion.

In a stinging critique of that decision, Mr Chapman said that Origin's management overstated the value of its assets and suggested that Origin's valuations had not factored in the significant risks of commercialising CSG reserves - which requires investment in the billions of dollars.

He said: “Having reflected, [we] remain confident that our current offer is compelling. We have, therefore, decided to put that offer directly to Origin shareholders.”

Analysts said there was room for debate over which party had valued Origin correctly, and market insiders welcomed the fact that BG has not said that this is a final offer, leaving room to raise the bid if necessary.

“It's not our intention to raise our price but we reserve the right to do so,” Mr Chapman said. David Thomas, an analyst for Citigroup Global Markets, said in a note: “A significantly higher offer would not have sat well with BG's shareholders.”

Origin did not comment on the bid, but has advised shareholders to take no action on the latest offer. Shares in BG fell more than 2 per cent, to £12.36 yesterday. Origin shares jumped nearly 6 per cent to A$16.42.

With commodity prices on the rise, Australian resource companies are in high demand. On Monday, the Chinese steel maker Baosteel agreed to a near-doubling of the price it would pay Rio Tinto for iron ore. The Japanese steelmaker Nippon Steel, and Posco, its South Korean rival, are under pressure to reach similar deals.

BG Group's offer is based on a minimum acceptance level of 50.1 per cent. It said that it would fund the deal through a combination of cash reserves and a syndicated loan from a consortium of European banks.

Gas meter

— Methane is the principal energy source in natural gas

— Coal bed methane, or coal seam gas, is retained on the surface of the coal in micropores

— China used 1.4 billion cubic metres of coal bed methane in 2006 — 3 per cent of its natural gas consumption

— Beijing wants to increase that to 10 per cent by 2010

Times Recommends

• Minister in talks with Saudis to protect creditors
• Premier Inn hits back in £29-a-room row
• Bankers hit back at 'populist' bonus supertax