US-based consultancy Bain & Co has denied allegations by former partner Athol Williams that it has not been forthcoming in disclosing its role in the damage inflicted during management battles at the SA Revenue Service (Sars).

It also reiterated that when it did work at Sars it had no intention of weakening the tax agency, despite judge Robert Nugent’s commission finding that Bain colluded with former commissioner Tom Moyane, to do so.

Williams, a University of Cape Town lecturer, had publicly resigned during an finance conference in Sandton earlier in October, citing a lack of transparency from Bain as it deals with the reputational damage its work at the revenue agency.

Bain said in a statement on Monday that Williams had made his intentions to leave the firm known in August, citing a need to focus on his PhD studies and lecturing work.

“We have conducted a thorough investigation into all aspects of our engagement with SARS. This investigation, which is now complete, did not find any evidence that Bain was involved in any scheme with Mr Moyane to damage Sars or that Bain withheld relevant evidence of any kind,” the statement read.

“We disagree with any assertion that the firm has not disclosed its full role in the events that transpired at Sars,” Bain said.

Bain said it had reaffirmed its commitment to fully co-operate in any investigation in July, and while it had made mistakes, it had “no motive, monetary or otherwise, to damage Sars”.

In the aftermath of Jacob Zuma’s presidency, Bain became one of the highest-profile faces of alleged state capture together with McKinsey and KPMG.

The company, one of the world’s top three consultants, stands accused of weakening Sars so that it missed its revenue targets, contributing to the country being saddled with a VAT increase for the first time in a decade.

The company had brought in Williams and retired deputy chair of Anglo American SA Norman Mbazima to oversee the implementation of remedial action after the Sars debacle.

The Nugent commission’s report of 2018 said there were two corruption schemes that Bain was part of at Sars.

The smaller scheme was Bain’s attainment of the tender to restructure the tax agency irregularly. And the bigger scheme “can be described as a premeditated offensive against Sars, strategised by the local office of Bain & Co, located in Boston, for Mr Moyane to seize Sars”, the report said.