This follows the leaking of a cache of data to the International Consortium of Investigative Journalists in Washington. Its stories have had worldwide ramifications and embarrassed business leaders and politicians across the globe. Now, a Fairfax investigation can reveal that more than 500 Australians feature in the 2.5 million documents.

The documents were independently leaked to tax authorities in Australia, Britain and the US, which together have already launched investigations in what might become the biggest international tax probe in history.

The leaks stem from two overseas wealth management companies - Commonwealth Trust Ltd in the British Virgin Islands and Portcullis TrustNet, an Asian-based company offering services in tax havens stretching from the Cook Islands to the Seychelles.

The Tax Office has confirmed two individuals are already the target of a criminal investigation, and has requested information and documents from at least 40 other people.

The Herald is not suggesting that all the Australians who appear in the overseas data and whom it has named in its coverage have been involved in illegality as taxpayers can hold offshore accounts for a number of legitimate reasons, such as facilitating international business transactions.

Among the prominent Australians with overseas companies are David Mortimer, the former chairman of Leighton Holdings and Australia Post, and the former chief executive of TNT.

Celebrated chef Tetsuya Wakuda and Melbourne mining supremo Owen Hegarty have each had companies in the British Virgin Islands while philanthropist Janet Holmes a Court, once the richest woman in the country, has previously had a company in the Cook Islands.

A web of overseas structures was also employed by Tim Johnston and other directors of Firepower, which fleeced $100 million from investors with the false promise of a pill that would reduce cars' fuel consumption.

The documents show corporate criminal Tony Senese incorporated a company in the Cook Islands shortly before being jailed in Melbourne for seven years on 25 charges of false accounting.

Justin Breheny, an executive with insurance giant IAG, used his British Virgin Islands company to buy shares in an unknown company while Double Bay businessman Colin Sim also had interests in offshore companies.

Jefferson and Aileen Cheng, who had criminal charges against them dropped over the construction of the Ninoy Aquino International Airport terminal in the Philippines, also had a complex web of offshore companies.

Colourful businessman Karl Kazal confirmed he set up two offshore companies to handle distribution of hospital equipment from the United Arab Emirates but said the offshore accounts were never operational.

A West Australian organised crime figure, who cannot be named because he is about to face trial for a major drug importation, is on the list, along with Michael Milne, who is serving an 8½ year jail term for money laundering and dealing with the proceeds of crime.

The Sydney businessman was one of the initial targets of Project Wickenby, a multi-agency taskforce comprising the Australian Crime Commission, the federal police and the Tax Office.

The Herald has confirmed that Project Wickenby will handle some of the fresh investigations.

Greg Williams, the Tax Office's deputy commissioner of serious non-compliance, said: ''The people who are involved in this, it is not the man in the street. It is not the average salary and wage earner. It is people who are wealthy enough to make this behaviour potentially worthwhile for them.''

But if they have failed to declare taxable income, Mr Williams said ''the time to come forward is now if you have concerns about something you might have done''.

Islands home to holding

Following the 1990 death of her millionaire husband Robert Holmes a Court, a well-known corporate raider, Janet Holmes a Court took over the management of the family company Heytesbury, which ran several cattle stations and a horse stud, along with construction, theatre and wine interests.

In 2000, her eldest son, Peter Holmes a Court, left to pursue his own interests, leaving his mother and younger brother Paul to run Heytesbury. Peter Holmes a Court's 16 per cent holding in the family company was sold to RM Investment Limited, which Mrs Holmes a Court had set up in the Cook Islands.

''Please be advised that Mrs Holmes a Court's appointment as the sole director of the Company was lodged with the Registrar's office on the date the company was incorporated, 22 March, 2000,'' said an email to Mrs Holmes a Court's solicitor, John Pickering.

The two shareholders in the company were Mrs Holmes a Court and her son-in-law Robert Mather. Later emails were sent to the Cook Islands providing Paul Holmes a Court's change of address so that the files could be updated.

There is no suggestion that RM Investment, a wholly-owned subsidiary of Heytesbury, did not meet its tax obligations. The company filed annual returns with ASIC.

In November 2006, Heytesbury's company secretary, Keith Murray, sent an email to the Cook Islands saying: ''We have decided to dissolve the Company, on the basis that it has no ongoing function or purpose within the Heytesbury Group.''

In an email to Fairfax Media, Paul Holmes a Court said ''I have never established a company in the Cook Islands'' but he declined to comment on whether he had an interest in any offshore entity. Mrs Holmes a Court did not reply to inquiries.

Chef went from shop to offshore company

He arrived in Sydney in 1982 penniless and with little English. In a decade, Tetsuya Wakuda was a household name and his restaurant, Tetsuya's, was eventually acclaimed as one of the top 50 in the world.

Wakuda got his start on Sydney's restaurant scene washing dishes in one of the city's best seafood restaurants.

He struck out with a couple of financially precarious ventures before opening the restaurant that bore his name in 1989.

At 125 square metres, it was a poky shopfront in a suburb not yet touched by gentrification. It was soon booked out for weeks and he was feted with accolades.

In 2000, he traded up and his financial affairs became more complex.

His dream restaurant was more than 15 times his tiny Rozelle address and was in a heritage-listed building on Kent Street. It had a massive kitchen and a secret entrance for famous diners.

And, about six months after it opened, in early 2001, a company was incorporated offshore, listing him as a director. His restaurant's Kent Street address was provided.

Records show ''Double Win Trading Ltd'' was registered in the British Virgin Islands jurisdiction and that Portcullis offered one of their companies, Gurker Limited, to be a director of Wakuda's company.

In January 2006, Portcullis' corporate adviser in Singapore sent an email asking to get ''the client's authorisation'' to invoice the HSBC Private Bank (Suisse) in Singapore on behalf of Double Win Trading.

The chef did not reply to Fairfax's inquiries.

Virgin Islands venture behind investments

In late November 2007, one of the titans of Australian industry, David Mortimer, who was the chairman of construction firm Leighton Holdings at the time, set up a company in the British Virgin Islands.

According to the notes on his personal file with Portcullis, David Allen Mortimer, who had provided his passport details, was ''ex-CEO of TNT'' and was running a private equity company Crescent Capital.

''Nature of business - investments in financial market. Source of funds from savings, salary and bonuses accumulated,'' Portcullis noted.

His company in the British Virgin Islands, Beaune Finance, was set up by the Singapore office of UBS in mid November 2007, and two weeks later was transferred to Portcullis, which provided another company Execorp to be the sole director of Mr Mortimer's company.

When first approached by the International Consortium of Investigative Journalists earlier this year, Mr Mortimer said he had never heard of Beaune Finance and suggested his association with it may have been a case of mistaken identity.

When Fairfax Media asked Mr Mortimer to confirm the company was his, he replied by email earlier this month: ''The company you refer to was set up but was liquidated some time ago.''

He did not respond to further questions including when the company was liquidated.

Apart from his chairmanship of Leightons, Mr Mortimer has previously been managing director of transport company TNT, chairman of Sydney Airports Corporation and a director of Australia Post and Ansett.

In December, Mr Mortimer, along with former royal commissioner James Wood and ex-NSW police commissioner Ken Moroney, was appointed to the Customs Reform Board, which was established in the wake of allegations of widespread corruption among customs officials.

Do you know more? investigations@smh.com.au