David Cameron has "no choice" but to resign in the face of revelations that he had a profitable stake in his father's offshore investment fund, an MP has claimed.

John Mann, Labour MP for Bassetlaw in Nottinghamshire, has called on the Prime Minister to step down from office after "failing to be honest" with the voting public on several occasions.

Mr Mann, a high-profile campaigner for tax transparency, told Sky News: "It's taken six attempts for journalists to get this out of Mr Cameron - who didn't recall Parliament to allow us as MPs to question him.

"The question is one of honesty here, he's covered this up [...]

"The key issue is, he failed to tell parliament, he failed to declare it, he failed to tell the British people standing for Prime Minister."

The revelations came after a huge leak of documents from the Panama-based firm Mossack Fonseca, a law firm and corporate services provider which appears to have enabled clients to hide billions of dollars in tax havens.

After his father was listed as one such client, Mr Cameron was forced to issue a number of statements about the benefits he and his family enjoyed from the offshore fund, with Downing Street first saying that it was a "private matter".

He then stated that he had "no shares, no offshore trusts, no offshore funds" and would not have any in the future.

John Mann has said it took "six attempts" by journalists to get the full truth out of David Cameron (Press Association)

Questions about the past were raised, however, resulting in Mr Cameron confessing in interview with ITV News that he had shares in his father Ian's tax haven fund that he sold for £31,500 just before becoming Prime Minister in 2010.

His father's company, Blairmore Holdings, paid no tax in 30 years.

The PM also admitted he did not know whether the £300,000 he inherited from his father's will in 2010 had also benefited from the tax haven status.

Mr Mann added that Jimmy Carr, who used a legal tax loophole to pay as little as one per cent tax on his earnings, would think the Prime Minister hypocritical for criticising the comedian's actions as "morally wrong" while himself having benefited from such arrangements.

"He's got to resign, he's got no choice," said Mr Mann. "It's very, very straightforward."

Edward Snowden, who disclosed information about the scale of global surveillance programmes, has also tweeted in the wake of revelations: "The next 24 hours could change Britain."

Mr Snowden also implied the British public should protest effectively rather than simply hope something would be done, saying "with respect, hope is not a strategy."

A protest against Mr Cameron is planned for 9 April outside Number 10 Downing Street, according to a group on Facebook.

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At the time of the revelations about Jimmy Carr's tax avoidance measures in 2012, Mr Cameron said: "The government is acting by looking at a general anti-avoidance law but we do need to make progress on this.