Labour has stepped up demands for an independent inquiry into the Panama Papers leak after it emerged the head of HM Revenue and Customs (HMRC) was previously a partner at a law firm which represented a number of offshore companies - including Blairmore Holdings, the fund set up by David Cameron's father.

HMRC has been given in a lead role in the £10 million taskforce launched by Mr Cameron to investigate allegations of wrongdoing linked to the Panama Papers leak of more than 11 million files from Panamanian law firm Mossack Fonseca.

Edward Troup, the new executive chairman of HMRC, is a former partner at Simmons & Simmons, whose clients have included the Panama-registered fund created by the Prime Minister's father Ian, the Guardian reported.

The newspaper, which has access to the leaked information, said Simmons & Simmons' name appears on dozens of emails and documents in the Panama Papers in connection with a number of companies registered with Mossack Fonseca.

HMRC said Mr Troup had never had dealings with Mossack Fonseca and none of the individuals or organisations named so far in relation to the Panama Papers were clients he had advised.

But the shadow chancellor, John McDonnell, seized on the Guardian report as a further indication of why the inquiry into the Panama Papers revelations should be independent.

He said: "This further highlights why, for any inquiry to have the full confidence of the British people, it must be truly independent in structure and process.

"It certainly should not be reporting to politicians whose party has been highly implicated in this scandal, with large donors directly involved in this matter.

"But most of all it needs to be above question and beyond rebuke. And with new allegations calling the Government's approach into question the only obvious answer is a truly independent public inquiry as Labour is demanding."

The Guardian, which has access to the leaked data, said Simmons & Simmons' name appears on dozens of emails and documents in the Panama Papers in connection with a number of companies registered with Mossack Fonseca.

Mr Troup worked at the firm from 1997 until 2004 and the Guardian reported that some correspondence dates back to 2003, when Mr Troup was still a partner.

A HMRC spokesman said: "Before joining the Civil Service in 2004, Edward Troup had a successful career in the private sector, during the course of which he dealt with many companies.

"He can confirm that he never had any dealings with Mossack Fonseca, was unaware of the company until recently, and that none of the individuals or organisations named so far were clients that he advised.

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"Edward Troup's role in HMRC has never involved responsibility for operational activities or direct dealings with companies on their tax affairs.

"In any event, the governance in place at HMRC means that any commissioners who have a potential conflict of interest would exclude themselves from any investigation or settlement involving a taxpayer with which they had had dealings in their previous careers."

The first emails to Mossack Fonseca regarding Blairmore date from 2005 and the Guardian reported that Simmons & Simmons was advising Blairmore from 2001

The Panama Papers appear to show Simmons & Simmons' offices in London and Hong Kong were registered as clients or intermediaries with Mossack Fonseca.

The newspaper reported that In 2008, when Blairmore was considering a change of jurisdiction, Simmons & Simmons asked Mossack Fonseca for advice on the benefits of other tax havens.

