Damning evidence linking Leighton Holdings to allegedly corrupt payments has emerged in a court case that reveals how Leighton agreed to pay ''not less than $25 million in marketing fees'' to a Monaco firm to help win Iraq government projects, even though the projects required no marketing.

Leighton's own lawyers recently labelled these payment agreements as ''vague and uncertain'', while corporate corruption expert ANU Associate Professor Katherine Hall, who reviewed them at Fairfax Media's request, said they were risky and compared them to the dealings of AWB Limited in Iraq over a decade ago.

Leighton Holdings: $25 million in marketing fees under question. Credit:Glenn Hunt

Files from the British High Court of Justice case reveal that the fees were contained in deals, known as memorandum of agreements (MOAs), struck between Leighton's offshore business and Unaoil in the last half of 2010 and early 2011 in a bid to secure oil pipeline contracts in the south of Iraq.

Unaoil operates out of Monaco but is incorporated in the British Virgin Islands, a notorious tax haven.