LONDON--An independent U.K. shareholder advisory group wrote a letter to U.K. Business Secretary Vince Cable on Thursday requesting the government launch a formal investigation into the operations of troubled miners Bumi PLC (BUMI.LN) and Eurasian Natural Resources Corp PLC (ENRC.LN).

In a letter seen by The Wall Street Journal, PIRC said the government should use its powers under the Companies Act. The government has done so in the past when the U.K.'s former Department of Trade and Industry launched investigations into the Mirror Group and hotel group Queen's Moat.

The PIRC letter was first reported by The Telegraph newspaper on Friday.

PIRC said in its letter that "both companies are U.K. registered companies, but both are in the ludicrous position of commissioning investigations into themselves, when the directors of the parent companies themselves may well have cases to answer."

The companies have been embroiled in board room spats about corporate governance and conducted their own investigations into whistleblower allegations of wrongdoing while keeping the U.K.'s Serious Fraud Office abreast about their findings.

In the case of Kazakhstan-focused miner ENRC, the fraud office decided this week to launch a formal investigation into allegations of fraud, bribery and corruption at the company's Kazakhstan and African operations following months of dialogue with the company.

The formal investigation comes on the same week that ENRC's Chairman Mehmet Dalman resigned unexpectedly following the departure of a series of high-level executives.

The FTSE-100 miner's shares are down more than 50% since it was listed in London in 2007, due in part to board room spats regarding the influence of the founding shareholders over the company and other corporate governance concerns.

In the case of Indonesian coal miner Bumi, an anonymous whistleblower's allegations of financial irregularities at one of Bumi's Indonesian subsidiaries--Bumi Resources (BUMI.JK)--prompted a continuing struggle over the parent company's governance.

Earlier this week, Bumi PLC requested a temporary suspension of trading in its shares because its 2012 financial results missed a disclosure deadline as the company investigates the integrity of balance-sheet information at its other Indonesian subsidiary, Berau Coal Energy (BRAU.JK).

Bumi's shares are down more than 70% since its 2010 listing under the name Vallar.

PIRC also called for ENRC's shares to be suspended.

"It has been clear for sometime that the affairs of both Bumi and Eurasian Natural Resources Corporation fall short of the standard expected of U.K. listed companies," the shareholder advisory firm said. It said the problem stems from the "over-liberalisation of the listing regime when the U.K. Listing Authority was under the control of the ineffective Financial Services Authority, and the newly listed London Stock Exchange was pulling in lower quality companies on a volume and fee driven basis."

PIRC said that if the U.K. government is unable to bear the costs of the investigation in the current difficult environment, then the department should request that the LSE bears the costs.

"It is the LSE that was responsible for, and had profited from, bringing such companies to the London market," PIRC said.

In a statement, ENRC said it "is committed to a full and transparent investigation of its procedures and conduct."

The LSE declined to comment. A representatives for Bumi wasn't immediately available following the close of business hours.

Write to Alex MacDonald at alex.macdonald@dowjones.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires