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The insolvency regulator has launched a corruption investigation into the liquidation of a group of printing companies by the international accountants Grant Thornton, The Sunday Times can reveal.

The rare move follows allegations by a member of the creditors’ committee that directors of the insolvent printing group “bribed” him to vote in their favour and to stop asking questions about the liquidation.

Earlier this month, investigators at Lord Mandelson’s Department for Business, Enterprise and Regulatory Reform (BERR) began examining a dossier of internal documents and witness statements. The file includes the alleged “bribe contract” and evidence that shortly after receiving it the creditor was wired £37,500 from Grant Thornton’s client account.

As well as examining the directors’ conduct, investigators will look at the actions of the liquidator, Andrew Hosking. The Insolvency Practitioners Association, on whose council Hosking sits, is also looking into the case.

Disclosure of the BERR corruption probe is an embarrassment for Grant Thornton, which provides auditing services to local government, NHS trusts and blue-chip firms. Hosking, a senior partner at the firm, is also involved in clearing up the UK fallout from the Bernie Madoff fraud.

The cash-for-vote allegations come amid a separate industry-wide inquiry by the Office of Fair Trading into whether creditors are being ripped off by poorly regulated insolvency practitioners when companies collapse.

OCP, the printing company at the centre of the bribery allegations, provided marketing material to banks and mobile phone companies until its collapse in 2006. The company took three years to liquidate. Grant Thornton charged more than £1m in fees for this and two earlier liquidations of related firms. Unsecured creditors, including the taxman, lost more than £650,000 as a result of the companies going bust.

This March, a High Court judge appointed a new liquidator, who upon examining Grant Thornton’s files made a formal complaint to BERR.

Stephen Hunt of Griffins described what he had seen as “disturbing”. In a complaint letter he also wrote: “There are common denominators, namely some of the directors, the accountant and the administrator who supervised all three liquidations.”

The alleged bribe agreement, dated October 24, 2006, was marked “confidential” and given to a retired OCP director, Stan Ovenden. It offered him £37,500 in return for his vote to pay two directors a large share of £165,000 sitting in a bank account.

The agreement, seen by The Sunday Times, also placed other possibly illegal demands on Ovenden as a member of the creditors’ committee. It required him to stop asking further questions about a range of matters including directors’ loans, claims of trading while insolvent and a £1.3m payout from an earlier liquidation.

The cash-for-vote agreement also required that Ovenden sack his lawyers and Griffins and that he stop suggesting there was any conflict of interest in Grant Thornton’s role.

After taking legal advice, Ovenden played along and signed the agreement. He also pretended to call off Griffins and voted to allow Grant Thornton to release the £165,000. Weeks later, the alleged bribe money was wired into his personal account.

After reviewing all the papers, a prosecution lawyer at BERR decided in May that the department would launch “a criminal investigation into the allegation of corruption”. So far it has been discreetly gathering evidence but interviews with the directors and Hosking are expected in the new year.

Philip Thompson, the director at the centre of these events, admitted to The Sunday Times that he drafted the confidential cash-for-vote agreement, but insisted that he had cleared his actions with Grant Thornton and his own lawyers.

“It was effectively a payment to [Ovenden] so he would stand aside and let the money be released,” he said. “I suppose it is a bribe if you like. One man’s bribe is another man’s commercial agreement . . . But I didn’t do it without asking questions of the relevant people. If I’m upfront about it am I therefore doing something illegal? And everybody said, ‘Well, it may be immoral but if you are upfront about it, it’s not illegal’.”

Hosking declined to explain what he thought the £37,500 payment to Ovenden represented.

In a statement, Martin Ellis, a managing partner at Grant Thornton, said the allegations were “entirely without foundation and entirely rejected”.

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