Financier Nathaniel Rothschild has resigned from the board of miner Bumi, saying he had lost confidence in the management's ability to stand up for investors.

In his resignation letter he accused the company's Chairman of being "complicit" in oppressing minority shareholders.

It is the latest twist in a battle between Rothschild, who helped create the company in 2010, and the influential Bakrie family from Indonesia.

Last week the Bakries put a deal on the table that could have put an end to the fierce boardroom rift and ongoing concerns over corporate governance.

The company is currently investigating alleged irregularities at Bumi Resources, in which it has a 29% interest.

The Bakries proposed swapping their stake in Bumi for a stake of equivalent value in Bumi Resources, thus ending the relationship between Bumi and themselves.

However, in his resignation letter to Chairman Samin Tan, Rothschild said it would be a "disgrace to proceed with, or even entertain, the proposal" while the investigation at Bumi Resources was ongoing.

"You appear determined to drive through the Bakries' proposal," wrote Rothschild.

"I believe that this proposal is so obviously not in the interests of minority shareholders that I find it impossible to stay on as a director. I am afraid that I have lost confidence in the ability of the Plc board to stand up for investors."

Tan became chairman earlier in 2012 after buying half the Bakries' stake in Bumi.

Chris Fong, a Bakrie spokesman, told the Financial Times that Rothschild's resignation letter as "unfair, unreasonable and ridiculous".

"He's the one who came to us," Fong told the newspaper. "We came to London in good faith. We offered our business to him. He did the due diligence. We were very transparent and we put our own money in. In the end the truth will be told."

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