Dennis Christopher Carter Lunn, known as Christopher, ran a Sussex-based accountancy firm, Christopher Lunn & Co, whose 7,000-plus clients included many from the media and entertainment worlds.

The firm was investigated by HM Revenue and Customs and in 2010 the premises in Crowborough were searched and Lunn was arrested.

HMRC explained that it had uncovered evidence of a range of serious offences, which included the inflating of accountancy fees and the fraudulent use of trading losses – all intended to help Lunn and his clients evade paying their fair share of tax.

Lunn stood trial at Southwark Crown Court in September 2013, charged with six counts of cheating the public revenue. In January 2014, Lunn was acquitted on two charges while the jury was unable to reach a verdict on the remaining four.

However, after five years of investigation, Lunn was convicted at the retrial, where a jury found him guilty of four counts of cheating the public revenue. He will be sentenced on 6 January 2016.

Simon York, director of the Fraud Investigation Service, HMRC said: “Lunn believed he could make up fraudulent claims to benefit both himself and his clients.

“Hard work from HMRC officers across the department proved him wrong. This long-running investigation has already recovered £20m, as Lunn’s former clients settle their tax liabilities, with more to come.

“I hope this result serves as a reminder to those who try to cheat the public purse – particularly those in the tax profession – that no one is above the law and that HMRC will relentlessly pursue tax evaders to bring them before the courts.

“As Lunn’s clients were unaware of his actions, they have been offered a chance to put things right for themselves, by paying any tax and interest due. Any client who has not yet come forward pending the outcome of the trial is encouraged to speak to HMRC to bring their affairs up to date as many of Lunn’s clients have already done.”

Lunn's son, Christopher Jonathan Lunn (known as Jon), who also worked at the firm, was convicted in December 2014 on six counts under the Fraud Act, after he had sent false invoices to HMRC to try to cover up the fraud in the practice.