David Cameron is under pressure to order an investigation into those named in the Panama papers, including his own family, as the biggest data leak in history claimed its first political casualty.

Sigmundur Davíð Gunnlaugsson, the Prime Minister of Iceland, resigned 36 hours after it emerged that his wife held secret interests in the country's bailed-out banks.

Mr Cameron also faced increasing questions about his own family's affairs.

The Prime Minister was forced to issue two statements in as many hours about his own tax returns and those of his wife, Samantha.

But critics claimed both failed to answer whether or not Cameron family money was still being held overseas.

Meanwhile, Labour leader Jeremy Corbyn called on the Prime Minister to impose direct rule on British overseas territories and Crown dependencies acting as tax havens.

The idea was backed by the former Business Secretary Vince Cable who said that Mr Cameron should not be “bullied by rogue micro-states”.

Mr Corbyn also called for an independent investigation into all Britons linked to the panama papers, including Mr Cameron’s late father.

Ian Cameron helped launch Panamanian firm Blairmore Holdings, named after the family home in Aberdeenshire, which reportedly paid no UK taxes for more than three decades.

Labour said that Mr Cameron must "lead by example" and "set the record straight" on his own tax affairs.

On Monday Downing Street refused to disclose if the Cameron family still had funds in offshore investments, saying the issue was a "private" matter.

But one of Mr Cameron’s own ex-ministers, former Attorney General Dominic Grieve, warned that there was a "need for transparency" from public figures.

Mr Corbyn said: "It is not a private matter if tax has not been paid. An investigation must take place, an independent investigation."

He added: "I think the Prime Minister, in his own interest, should tell us exactly what's been going on."

The Labour leader also piled pressure on the Prime Minister by offering to publish his own tax return.

Mr Cameron has previously indicated that he would release his tax details – although that idea was later ditched.

Within hours Mr Cameron was tackled about the issue at a 'town hall' style meeting in Birmingham.

He declared that he had "no shares, no offshore funds, nothing like that”.

But critics accused him of dodging the question of whether or not Cameron family money was held overseas.

Within hours Mr Cameron was forced to release a second clarification, which also failed to appease his opponents.

In a statement, a No 10 spokesman said: “To be clear, the Prime Minister, his wife and their children do not benefit from any offshore funds.

“The Prime Minister owns no shares.

“As has been previously reported, Mrs Cameron owns a small number of shares connected to her father’s land, which she declares on her tax return.”

Meanwhile, Oxfam called on the Prime Minister to clean up Britain’s "dirty offshore backyard".

Royal Bank of Scotland was among those drawn into the growing row after it emerged that RBS-owned bank Coutts Trustees was reported to have helped clients set up complex offshore structures.

Meanwhile, a Edinburgh-educated banker, Nigel Cowie, denied wrongdoing after it was reported that he set up a secret offshore finance company with links to the North Korean regime's nuclear weapons programme.

Scots tycoon Scot Young, who was locked in a bitter divorce battle and died in 2014 after falling 60ft on to railings outside his London apartment, also reportedly used offshore tax havens to hide his wealth.

HSBC, Credit Suisse and UBS were among more than 500 banks, including subsidiaries and branches, which registered nearly 15,600 shell companies with Panama law firm Mossack Fonseca, according to the International Consortium of Investigative Journalists (ICIJ), which is releasing the documents.

HSBC said it was working closely with authorities to combat financial crime and has put sanctions in place.

A spokesman for Coutts Trustees said the bank was committed to the highest standards when complying with regulation.

ICIJ say that they will release the names of all companies listed in the files in early May.

Edward Snowden, the American whistleblower mocked David Cameron for claiming that his family's tax affairs were a "private matter", tweeting "Oh, now he's interested in privacy".

Internationally, China claimed reports that relatives of politicians, including President Xi Jinping, own offshore companies were "groundless".

There were also allegations that former Siemens managers may have kept hundreds of millions of dollars in the wake of a bribery scandal a decade ago.

And it was reported that aides to the French far-right politician Marine Le Pen aides had set up a “sophisticated” offshore system.

Close associates of Russian President Vladimir Putin, as well as Barcelona striker Lionel Messi, Oscar-winning Spanish film director Pedro Almodovar and actor Jackie Chan were among those named in the papers.