Sir Paul Judge, a former board member of FTSE-listed mining giant Eurasian Natural Resources Corporation (ENRC) - has countersued the firm for libel.
The announcement of the case comes after extensive legal wrangling between Sir Judge and the multinational, according to the Financial Times (FT).
Sir Judge alleges that a press release distributed by ENRC in July, which stated that he would be sued for breach of fiduciary duty over the supposed leaking of confidential information and documents, was defamatory and constituted libel.
In a statement released to the High Court in London, which was seen by the FT, Sir Paul said: "[The press release] was understood to mean that [Sir Paul] had deliberately and in bad faith, leaked ENRC secrets to the media on a number of occasions and in doing so had acted in breach of his fiduciary duty as a former non-executive director of ENRC and in light of this was not to be trusted in such a role."
ENCR denies this charge and commented that it has faith in the strength of its allegation that the ex-board member sent unauthorised documents to the Daily Telegraph and FT, as well as its ability to combat claims of defamation and libel.
Sir Paul's solicitor declined to comment on the case.
ENRC board members have a previous history of being embroiled in extensive court battles. All charges against Alexander Mashkevich, Patokh Chodiev and Alijan Ibragimov - three of the firm's biggest backers - were dropped in 2011 after a 15-year court battle in Belgium.
Prosecutors in the European country alleged that the men were involved in money-laundering and forgery - claims the trio flatly deny and were never convicted of.
The case was, according to the FT, settled outside of court before any verdict was handed and the three men have never admitted guilt.
By Chris Stevenson