It has been reported that KPMG wrote last week to approximately 500 existing and retired UK partners with estimates of their individual ‘worst-case’ liabilities, which in some cases run to several thousands of pounds.

The disputed tax dates back to 2010‎, and is understood to revolve around issues including the accounting treatment for an existing investment in one of KPMG's Middle East operations; its accounting for acquisitions in the UK, which were undertaken through its LLP firm; and other items where there was disagreement about the scale of eligible tax deductibility.

KPMG has not confirmed or denied the existence of the letters. In a statement, the firm said: ‘We will not comment on the specifics of our tax affairs. However, like most organisations KPMG is in regular discussion with HMRC as to our tax liabilities.’

‘In keeping with our tax principles, and our published tax strategy, we make full disclosures to HMRC on all tax aspects including those where the tax treatment is not clear either in law or guidance.

‘Again, like many large organisations, we will, on occasion, dispute HMRC's interpretation of tax law, particularly where it contradicts previous guidance or practice. Tax enquiries can go on for many years, with both HMRC and taxpayers consulting with tax law experts in particularly complex areas.’