Lord Malloch-Brown, a Labour minister under Gordon Brown and a former deputy secretary-general of the United Nations, is being sued by the Israeli billionaire Beny Steinmetz.
Mr Steinmetz alleges that Lord Malloch-Brown and FTI Consulting, the City PR firm he chairs, passed on confidential information about his mining company BSG Resources (BSGR) while acting as its adviser until last November.
The Labour peer is accused of colluding with the billionaire investor George Soros after he joined FTI in September 2010. Court papers allege: "At a time when Lord Malloch-Brown's firm [FTI] was engaged as a key adviser on reputational and other matters, he was behaving in a collusive and unlawful manner with Mr Soros and providing confidential information to Mr Soros. This culminated in Lord Malloch-Brown, under pressure from Mr Soros, procuring FTI's resignation from its account with BSGR in November 2012."
BSGR specialises in iron ore, bauxite and uranium. It has been investing in Guinea since 2006, but has had difficulties in the African state since Alpha Condé was elected President in 2010. He has reformed the country's mining industry, enlisting Mr Soros as an adviser.
According to Mr Steinmetz and his advisers, Mr Condé has stopped all mining development.
Dag Cramer, the chief executive of Onyx Financial Advisors UK, which is advising the claimants, said: "Whilst purporting to be acting in our best interests, Lord Malloch-Brown was in fact serving to cause us enormous damage by facilitating George Soros and his NGOs which, we believe, facilitated a campaign of smears and innuendoes.
FTI said it would "defend this claim vigorously". Mr Soros could not be reached for comment.