The board has asked its lawyers Macfarlanes to examine allegations of email snooping as part of its brief to investigate claims made in a dossier sent to a non-executive director last month – which plunged the company into crisis and resulted in Rothschild's resignation from the board.
One source close to the board said: "You've seen the allegations [made by Rothschild's estranged Indonesian partners, the Bakrie family] that certain email systems have been hacked … [the whistleblower's report is also] part of what the investigation is about in terms of the provenance of this information, whether it's accurate and indeed whether it's legal. It is being investigated where this information came from as it was put in the lap of one independent non-exec."
The news of the widening inquiry comes after the company publicly split into factions that are furiously slinging accusations at each other.
Last week Bumi's Indonesian backers stoked tensions by alleging "phones and emails had been hacked", while Bumi's chairman, Samin Tan, subsequently claimed Rothschild had suggested that he had "access to, and has been reading, [Tan's] emails". Rothschild denies having access to Tan's emails or any involvement in the whistleblower's report. Following Tan's claims, Rothschild immediately issued his own statement. His spokesman said: "The allegations are untrue and defamatory."
The latest details of the spat came as Bumi responded to criticisms from Rothschild by saying it would not recommend an offer to carve up the group until the Macfarlanes inquiry is near completion, which is not expected until next month.
It also came as the Financial Times reported that Tan had said he was "aware of various allegations of financial irregularities at Bumi plc's Indonesian businesses a year before the London group launched its investigation last month".
Tan invested about $1bn (£620m) buying half the Bakrie family's Bumi stake last October, despite learning during due diligence of the some of the issues now being investigated by McFarlanes. A Bumi spokesman declined to respond to why its chairman had not launched an investigation before now.
The crisis kicked off last month when Bumi's shares crashed by a quarter in a single day after the mining investor hired Macfarlanes to investigate allegations of financial dishonesty at its main affiliate, one of Indonesia's biggest coal producers.
The news was followed by an offer from Rothschild's original partners in the Bumi float, the Bakrie family, to sever their tie-up by paying $1.29bn cash in return for Bumi's mines plus cancelling the family's own shares in the London-listed investment vehicle. The Indonesians also spiced up their proposal with a separate suggestion that Rothschild should give up a stake in Bumi worth upwards of £40m.
Rothschild opposed all aspects of the offer and followed that stance by announcing his resignation from the Bumi board on Monday – although it later emerged that both Tan and the company's non-executive, the former British diplomat Lord Renwick, had threatened to quit if Rothschild chose to stay.
Rothschild led the London flotation of Bumi two years ago, when it was known as Vallar and the shares began trading at £10 each. It started life as a £700m cash shell intended to make acquisitions in the mining industry and was renamed Bumi after taking a 29% stake in the mining business controlled by the Bakrie family. The shares closed up slightly at 254.39p.
If the Bakries' proposals to break up the company are accepted, it would leave Bumi as a cash shell again, in which case analysts expect the firm would be wound up. Such an outcome would crystallise a large loss to original shareholders, although it would represent an improvement on their position at the end of last month when the shares languished below 150p.
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