Australia and France have also said they will look into the operations of firms which have passed through the hands of Panamanian law firm Mossack Fonseca, while HMRC pledged to react “swiftly and appropriately”.
More than 11 million documents from the secretive legal company were passed to German newspaper Suddeutsche Zeitung and shared by the International Consortium of Investigative Journalists (ICIJ) to 107 media organisations including The Guardian and BBC’s Panorama.
The ICIJ found that the law firm helped a total of 33 clients who were subject to US sanctions, including companies based in Iran, Zimbabwe and North Korea, including one linked to North Korea’s nuclear weapons programme.
It also named Conservative peer Baroness Sharples, former Tory minister Michael Mates and ex-Tory donor Lord Ashcroft as being included within the leaked documents, as well as the father of Prime Minister David Cameron.
Rami Makhlouf, a cousin of Syrian president Bashar al-Assad and one of Syria’s richest businessmen, is named as someone for whom Mossack Fonseca was fronting various companies.
Sanctions were placed on him eight years ago by the US treasury, which claimed him to be a “regime insider” and someone who “manipulated the Syrian judicial system and used Syrian intelligence officials to intimidate his business rivals”.
HMRC said it had approached the ICIJ to request access to documents it has been handling over the past year.
Jennie Grainger, HMRC’s director-general of enforcement and compliance, said: “We will closely examine this data and will act on it swiftly and appropriately.
“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. The dishonest minority, who can most afford it, must pay their legal share of tax, like the honest majority already does.”
The British Virgin Islands, which as a British overseas territory is administered by the Crown, has 113,000 shell companies registered with the Panamanian law firm at the centre of the leak, more than any other territory.
The UK is one of the five biggest sources of money flowing through Mossack Fonseca, whose clients include “dozens” of donors to British political parties, as well as six members of the House of Lords and three former Conservative MPs.
The documents feature 12 current or former heads of state, and at least 60 people linked to current or former world leaders.
Among those are close associates of the Russian president, Vladimir Putin, who are said to have been involved in a £1.4 billion money laundering ring.
The documents are also reported to show Mossack Fonseca set up a company used to launder money from the Brink’s Mat bullion heist near Heathrow in 1983.
According to reports, the prime minister’s father Ian Cameron, who died in 2010, ran an offshore fund that avoided ever having to pay tax in Britain by hiring Bahamas residents to sign its paperwork.
Ian Cameron was a director of Blairmore Holdings Inc, an investment fund run named after the family’s ancestral home in Aberdeenshire, which managed tens of millions of pounds on behalf of wealthy families.
Clients are said to have included Isidore Kerman, an adviser to Robert Maxwell, and Leopold Joseph, a private bank used by the Rolling Stones.
Asked yesterday whether the Cameron family still had offshore investments, Downing Street said it was a “private matter”.
Mr Cameron is understood to have built up a significant legacy which was inherited by the prime minister following his death.
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.
Mossack Fonseca said it had operated “beyond reproach” for 40 years and had never been charged with criminal wrong-doing.