Peter Hain, the former Labour minister, has accused Hogan Lovells of hushing up corruption by South African politicians and has reported the firm to the Solicitors Disciplinary Tribunal.

In a speech to the House of Lords, Lord Hain said the firm produced a “fatally flawed whitewash” when it was instructed to investigate claims that the South African tax agency's deputy commissioner, Jonas Makwakwa, and his lover embezzled the equivalent of £100,000.

Hain, who was raised in South Africa and campaigned against apartheid, used parliamentary privilege to accuse HogLove of having cleared Makwakwa "despite reams of evidence to the contrary". He said Hogan Lovell’s report resulted in the reappointment of corrupt officials so they could continue “their looting and dirty work of robbing taxpayers”.

Hain also tied HogLove's work to the wider political scandal which has already claimed the life of PR firm Bell Pottinger. He claimed the firm's report made it “complicit in undermining South Africa’s once revered tax-collection agency", and was "thereby effectively underpinning President Jacob Zuma and his business associates, the Gupta brothers and others, in perverting South Africa’s democracy". The peer said he had reported the firm to the SRA.

Coincidentally, in 2008 Hain was forced to resign as Work and Pensions secretary when he was accused of accepting his own dodgy £100k, in illegal campaign donations. The CPS elected not to prosecute.

Hogan Lovells responded with a furious statement that Hain's accusations were "unfounded" and "reflect a lack of understanding of the work we were asked to carry out". The firm said its remit was only to identify possible breaches of internal policies at the tax agency, which it was unable to do when PWC's report, upon which Hogan Lovells had to rely, could not confirm that the questionable money transfers were improper. HogLove said Hain had "ignored" the evidence the firm presented to him and "instead appears to have relied on inaccurate press reports in South Africa”.

"Anyone who wants to take the time to understand our limited role in this matter can very easily read about it on the Parliament’s website or our own”, continued the firm. “If Lord Hain does have evidence of corruption then that should be reported to the appropriate authorities in South Africa. We look forward to working closely with the SRA on any complaint made to them by Lord Hain”.