Nathaniel Rothschild, Bobby Gafur Umar and Eddy Soeparno in Singapore Reuters

Shares in coal export group Bumi Plc plunged in London trading Monday after the company confirmed it had launched an urgent investigation into financial regularities at its Jakarta-based division.

Bumi said the probe will focus on so-called development funds at PR Bumi Resources, Asia's biggest power-station coal exporter, in which it own a 29.2 percent stake.

"The extensive development funds in PT Bumi Resources Tbk and the one development asset in PT Berau Coal Energy Tbk were marked down to zero in the accounts of Bumi plc as at 31 December 2011, except for one investment with a carrying value of $39m in the consolidated financial statements," the company said is a statement Monday.

Bumi, one of the worst performing stocks on the London FTSE 350 Mining Index, has been hit by in-fighting and falling coal prices for most of the year. Shares in the group fell more than 35 percent in early London trading to 128 pence each, extending an 85 percent fall in the group's share prices since late March. The group floated on the LSE two years ago at £10 per share.

Last month, PT Bumi shares fell nearly 20 percent in two days in Jakarta after the company reported a first half loss of around $322m and revealed that an investment fund management group - PT Recapital Asset Management - failed to meet $231m payment owed to the miner. PT Recapital is run by Rosan Roeslani, who is also a Bumi board member who has been in constant conflict with founder Nathaniel Rothschild after he called for a "radical cleaning up" of PT Bumi's finances last year and said he was seeking "repatriation of funds deposited with connected parties".

Bumi Plc CEO Nalin Rathod warned last month that slumping coal prices would have a "material impact" on future profits.

Indonesia said Monday it was maintaining its 2012 forecast for coal production at 332m tonnes with around 250m tonnes slated for export; both figures were lower than previous estimates. A Bloomberg news poll published in August anticipates an 11 percent decline in coal prices in the final three months of the year, from $225 a tonne to $200 a tonne, as demand for steel slows in key European and Chinese markets.