Prime Minister David Cameron came under pressure to explain his family's financial affairs on Tuesday after the Panama Papers revealed his late father ran an offshore fund which avoided paying tax in Britain for 30 years.

Cameron's Downing Street office insisted it was a "private matter" whether the family still had funds in offshore investments, although a government source later told AFP that the prime minister himself did not have any such funds.

The revelations, which made front page news in most British papers, are embarrassing for the Conservative leader who has sought to lead international efforts to improve financial transparency and fight corruption.

His late father Ian Cameron helped found Blairmore Holdings Inc, an investment fund based in the Bahamas, in the early 1980s and he was reportedly one of five UK-based directors until shortly before his death in 2010.

According to leaked tax documents seen by The Guardian newspaper and the BBC, Blairmore retained up to 50 Bahamas residents each year to sign its paperwork to avoid paying tax in Britain.

"In 30 years, Blairmore has never paid a penny of tax in the UK on its profits," The Guardian said.

The fund, which was apparently named after the Cameron family's ancestral estate in Scotland, also used controversial bearer bonds -- shares that are owned by whoever physically holds the paper -- until 2006.

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There is no suggestion that the company acted illegally by hiring local staff or that the family did not pay British tax on any repatriated assets.

But the revelations are embarrassing for Cameron given his strong public stance on the issue, particularly coming just a month before London hosts a major anti-corruption summit on May 12.

Legislation forcing British companies to disclose who owns and benefits from their activities comes into force in June.

But opposition Labour leader Jeremy Corbyn demanded that the government "stop pussyfooting around on tax dodging".

"There cannot be one set of tax rules for the wealthy elite and another for the rest of us. This unfairness and abuse must stop. No more lip service. The richest must pay their way," Corbyn said.

The revelations form part of a global scandal prompted by the leak of 11.5 million confidential documents from the Panamanian law firm Mossack Fonseca, which specialises in creating offshore shell companies.