The High Court has blocked White & Case from acting for major Ukrainian client Victor Pinchuk, after the firm failed to identify a conflict of interest.

In a decision handed down on Friday (31 January), Mr Justice Field debarred White & Case from advising Pinchuk in a major commercial dispute against oligarchs Igor Kolomoisky and Gennadiy Bogolyubov.

A group of companies owned by Kolomoisky and Bogolyubov first sought the injunction in November, arguing White & Case could have obtained confidential information about the pair's assets and corporate structures when it accepted an instruction to advise on a restructuring exercise and preparation for an initial public offering (IPO) of one of those companies, Optima Industrial Management.

The firm's relationship with Pinchuk dates from September 2010, when London and Moscow partner David Goldberg started advising the Ukrainian and his management company on a dispute with Kolomoisky and Bogolyubov over a ferroalloy joint venture.

In April 2011, New York partner Colin Diamond was approached for the Optima instruction, which he accepted after an internal conflicts check and confirmation from Goldberg that the earlier Pinchuk dispute had been settled.

In May 2012, Goldberg and the "Pinchuk team" began evaluating potential claims against Kolomoisky and Bogolyubov, a decision Justice Field called "surprising".

"Mr Goldberg must have appreciated that White & Case might have won the Optima Engagement that was being pitched for when he was asked by Mr Diamond in April 2011 if there would be a conflict if White & Case acted on the Optima Engagement," he concluded in the Judgment.

In March 2013, White & Case put in place "ethical screens" between the Pinchuk and Optima teams, but Justice Field found that prior to this point, there was a distinct possibility that between April 2011 and March 2013, the Pinchuk Team could have come into possession of confidential information which could have been used in the Commercial Court action.

White & Case deployed a so-called 'neutral team' headed by London partner Jason Yardley, and including the firm's general counsel Philip Schaeffer, to investigate the claimants' allegations of conflict of interest.

The neutral team interviewed all 129 people involved in the Pinchuk case, 73 of whom were lawyers, who confirmed they had not discussed any aspect of the Optima representation with any member of the Optima team, had not accessed documents on the matter, and were unaware of the nature of the Optima transaction.

However, Justice Field concluded the neutral team's investigations were not thorough enough, and did not rule out the risk of a conflict of interest.

"The reasons for this decision that there was no conflict of interest have not been disclosed to the Court and I am bound to say that I find it hard to see any good justification for it," said Justice Field.

White & Case turned to Olswang and Fountain Court's Bankim Thanki QC and Tamara Oppenheimer for the injunction hearing, while the claimants were represented by Brick Court Chambers' Daniel Jowell QC and Richard Eschwege, who were instructed by Enyo Law.

A White & Case spokesperson said the firm was considering whether "improvements to its policies or procedures can or should be made".

In a statement, the firm added: "White & Case has an exemplary record in detecting and avoiding conflicts of interest and in safeguarding our clients' confidential information.

"We have robust policies and procedures that are underpinned by strong systems and regular training and support for our partners, lawyers and staff. While we are disappointed by the judgment, the judge did not find that any actual breach of client confidentiality had occurred."