Former Conservative MPs, peers and David Cameron's late father are among scores of people and politicians whose financial affairs have been exposed by a massive leak of data about offshore investments.
The leak of more than 11 million documents from the Panamanian law firm, Mossack Fonseca, casts an unprecedented light on the way the rich and powerful are able to use tax havens to shield their wealth.
Ian Cameron, the prime minister's father who died in 2010, is reportedly named as a client of the firm. Six members of the House of Lords, three former Conservative MPs and "dozens" of donors to UK political parties who have been shown to have had offshore assets – although none have so far been named.
He reportedly used the law firm to shield his investment fund, Blairmore Holdings Inc, from paying taxes in Britain.
There is no suggestion that this avoidance arrangement or others exposed by the leak were anything but entirely legal or that Mr Cameron's family did not pay the UK tax due on any repatriated assets.
Former Tory MP Lord Mates told the website his holdings in Caribbean property firm were not of "any value".
The leak also reportedly shows links to 72 current or former heads of state, including dictators accused of looting their own countries including Libya’s former leader Muammar Gaddafi and Syria’s president Bashar al-Assad.
The information was passed to the German newspaper Suddeutsche Zeitung and has been shared with 107 media organisations in 78 countries, including the Guardian and BBC's Panorama, under the leadership of the International Consortium of Investigative Journalists (ICIJ).
Among the reported disclosures are a suspected 2 billion dollar (£1.4 billion) money laundering ring run by a Russian bank and said to involve close associates of President Vladimir Putin.
In all, the Guardian said there were 12 national leaders among 143 politicians, their families and close associates from around the world who were shown to have been using offshore tax havens.
Others who have been caught up in the disclosures include Icelandic Prime Minister Sigmundur Gunnlaugsson who is facing calls for his resignation and a snap election over claims he had an undeclared interest in his country's bailed-out banks.
In China, The Guardian said, the families of at least eight current and former members of the supreme ruling politburo had been found to have hidden wealth offshore.
Twenty-three individuals who had had sanctions imposed on them for supporting the regimes in North Korea, Zimbabwe, Russia, Iran and Syria were said to have been revealed to have been clients of Mossack Fonseca.
While there is nothing illegal about using offshore companies, the disclosures are likely to lead to fresh calls for international reform of the way tax havens can operate.
In response to the allegations against Mr Putin, the Guardian said his spokesman Dmitry Peskov dismissed the investigation as an "undisguised, paid-for hack job" and warned Russia had "legal means" to defend his dignity and honour.
The BBC said that Mossack Fonseca had said that it had operated "beyond reproach" for 40 years and has never been charged with criminal wrong-doing.
Shadow Chancellor John McDonnell said the revelations were "extremely serious" and criticised Mr Cameron for failing to "end tax secrecy and crack down on 'morally unacceptable' offshore schemes".
"Cameron promised and has failed to end tax secrecy and crack down on 'morally unacceptable' offshore schemes; real action is now needed," McDonnell said.
Green Party leader Natalie Bennett said that at the summit "pressure will rightly be on for him to abolish all of the UK's tax havens".
"Can understand young people asking why they should pay back student loans, given corruption exposed," she tweeted.
Oxfam has called on the UK – which is hosting an international anti-corruption summit next month – to take a lead in "cleaning up" a system which was hurting some of the world's poorest people.
"This leak highlights the key role that UK-linked tax havens like the British Virgin Islands play in allowing a privileged elite to dodge paying their fair share of tax," said Oxfam's head of UK policy, Richard Pyle.
"People in the world's poorest countries pay the highest price for the billions of lost tax money when their governments are unable to fund life-saving healthcare such as midwives and vaccinations for children.
"The UK is in a unique position to help clean up the murky world of tax havens - starting by ensuring that the real beneficiaries of shell companies registered in the UK's Crown Dependencies and overseas territories, such as the British Virgin Islands, are revealed ahead of May's anti-corruption Summit in London."
Jennie Granger, HMRC Director General of Enforcement and Compliance, said: “HMRC can confirm that we have already received a great deal of information on offshore companies, including in Panama, from a wide range of sources, which is currently the subject of intensive investigation.
"We have asked the ICIJ to share the leaked data that they have obtained with us. We will closely examine this data and will act on it swiftly and appropriately."
She added that HRMC had brought in more than £2 billion from offshore tax evaders since 2010.
“Our message is clear: there are no safe havens for tax evaders and no-one should be in any doubt that the days of hiding money offshore are gone," she added.
"The dishonest minority, who can most afford it, must pay their legal share of tax, like the honest majority already does."
Ramon Fonseca, a co-founder of Mossack Fonseca, confirmed the documents were authentic and had been obtained illegally by hackers.
But he said most people named in the reports were not his firm's direct clients but were accounts set up by intermediaries. He said the firm did not engage in any wrongdoing.