LONDON - Accounting giant KPMG and one of its former partners, David-Costley Wood, have been fined for holding a major conflict of interest when they advised on the sale of British bed manufacturer Silentnight in 2011.

KPMG has been fined 13 million pounds ($18.05 million) by Britain's Financial Reporting Council and Costley-Wood 500,000 pounds. The accountancy firm was also severely reprimanded and ordered to appoint an independent reviewer to conduct a "root cause" review.

KPMG was advising on the sale of Silentnight to U.S. private equity company HIG Capital in 2011.

An independent tribunal which examined the case said KPMG's involvement with Silentnight was "deeply troubling" as it failed to act solely in its client's interests. It in fact acted in the interests of a party whose interests were "diametrically opposed" to those of Silentnight, the tribunal added.

KPMG said in a statement that its controls and processes have "evolved significantly" since this work was performed over a decade ago.

"We acknowledge the tribunal's findings and regret that the professional standards we expect of our partners and colleagues were not met in this case," the firm said. ($1 = 0.7201 pounds)

(Reporting by Abhinav Ramnarayan Editing by Rachel Armstrong) ((Abhinav.Ramnarayan@thomsonreuters.com; 0044 751 745 1044; Reuters Messaging: Twitter: @abhinavvr))