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Image source, ICIJ

It's quite difficult for an individual to set up an offshore bank account or shell company without the help of a cooperative lawyer and bank. 

In the case of the Panama leaks, we know who the lawyers were, but the banks involved are almost as revealing given recent history. Named are divisions of banks including HSBC, Credit Suisse and UBS - all of which have had recent brushes with the authorities over their customers' tax affairs. 

Of the 15,600 shell companies created by about 500 banks globally, HSBC and its affiliates created the most: 2,300 in total.

Transparency International tweets:

Want even more detail on the Panama leaks? Click here, external to read the International Consortium of Investigative Journalists' comprehensive overview.

The ICIJ is a global network of more than 190 investigative journalists in more than 65 countries, external who collaborate on in-depth investigative stories, external. It was founded in 1997 by American journalist Chuck Lewis.

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The individuals using these offshore companies were “trying to be very secretive” by taking advantage of the resources and tools available, the ICIJ's Marina Walker Guevara tells Today.

“Some people are using it for legitimate reasons, but that secrecy is also offered to a whole bunch of people who are taking advantage of it and not using it for the right reasons but for criminality,” she says.

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The leaked Panama papers have opened up the murky world of offshore finance as never before and includes the names of 140 politicians as well as business figures. 

Marina Walker Guevara, deputy director of the International Consortium of Investigative Journalists, tells Today one of the most important revelations is about the level of secrecy the offshore world provides and the extent to which politicians use tax havens to hide their finances.

Most of the politicians are from democracies, she says, with some from countries that have declared they want to end offshore tax havens.

“Some of the politicians have violated local rules around disclosure. In some other cases those offshore companies have been involved in more important types of criminality including bribery… using offshore companies to hold gold mines,” Ms Walker Guevara says.

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Richard Brooks, a former tax inspector who now works for Private Eye, tells Today the evidence in the Panama tax files is "damning".

"What this shows is that you can’t rely on tax havens and the people who operate there to open up about the deals they do," he says. 

"What really needs to happen is for the tax havens to close." 

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Much reaction in today's newspapers about the disclosures in the Panama tax files. 

The Daily Mail reports, external that among the revelations are that six members of the House of Lords and three former Conservative MPs had offshore accounts, although the only British politicians so far named are Lord Ashcroft (pictured), Tory peer Baroness Pamela Sharples and former Conservative MP Michael Mates. 

Dozens of donors to UK political parties had similar arrangements, the Mail reports.

Campaigners said David Cameron now faces a "credibility test", having promised to end tax secrecy four years ago, the report adds.

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Tax lawyer Jo Maugham QC, external says Mossack Fonseca's clients chose to use Panama for a reason.

"What Panama has offered – its USPs in the competitive world of tax havenry – is an especially strict form of secrecy, a type of opacity of ownership, and (if the reports of backdating are correct) a class of wealth management profession some of whom have especially compromised ethics. You go to Panama, in short, because, despite its profound disadvantages, you value these things.

And the question you should be asking is, what is it about this Mr X or that Mrs Y and his or her financial affairs that causes them to prioritise secrecy or opacity or (if the reports are correct) ethically compromised professionals above all else?

Perhaps it is not because the behaviour is criminal: tax evasion or money laundering or public corruption. Perhaps it is not. But – and especially in the case of Panama – very possibly it is." Read more here., external

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There are some extraordinary deals within the files, Richard Bilton of Panorama tells Today.

"Bear in mind, this company - Mossack Fonseca - promised absolute confidentiality, so these are arrangements that people thought would never be viewed by us, by the authorities, by anyone," he says

"Now they're very detailed - but to give you a flavour: the files reveal a suspected billion-dollar money laundering ring involving close associates of President Putin. 

"And the data shows how Icelandic Prime Minister Sigmundur Gunnlaugsson had an undeclared interest in an offshore company linked to his wife's wealth, though he says he did nothing wrong.

"There are also many more basic cases where individuals in the UK use Panamanian trusts and foundations to dodge tax on, for example property deals in London." 

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The scale of the leak of documents provides an unprecedented glimpse into the secret world of offshore finance, the BBC's Panorama reporter Richard Bilton tells Today. 

Mossack Fonseca offered financial services such as setting up foundations, trusts and nominee directorships, all of which can be used legally but were designed to help clients hide their wealth. 

The documents were leaked to the German newspaper Suddeutsche Zeitung and shared with the International Consortium of Journalists. The BBC and The Guardian are among 107 media organisations that have been analysing the documents. 

The range of clients is extraordinary: there are links to 72 current or former heads of state, including dictators such as Egypt's Hosni Mubarak and Libya's Muammar Gaddafi (pictured). 

They could be expected to figure, but the files also contain tax deals on behalf of democratically elected politicians and business leaders as well, Bilton adds.

More from Australian Tax Office deputy commissioner Michael Cranston, who says the data leak should serve as a warning to taxpayers.

"It's very hard to hide offshore and not have your assets and incomes not declared in this country," he told the ABC, external.

"Basically the message is don't do it, but if you have please come and speak to the tax office because ... penalties will be reduced significantly."

Tax authorities in Australia and New Zealand are investigating local clients of a Panama-based law firm at the centre of a massive data leak for possible tax evasion. 

The Australian Tax Office (ATO) said it is examining some 800 wealthy clients of Mossack Fonseca and more than 120 have been linked to an associate offshore service provider located in Hong Kong.

ATO deputy commissioner Michael Cranston said his office was working with the Australian Federal Police, the Australian Crime Commission and the anti-money laundering regulator. Some cases may be referred to the Serious Financial Crime Taskforce," he said. 

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Retail consultant Trevor Datson says it is a "little bit frustrating" that the loss of steel jobs seems to be taken more seriously than the loss of retail jobs.

Mr Datson, a partner at Etoile consultants, tells Today that retail contributes about £180bn to the UK economy and accounts for 4.5 million jobs if  wholesalers are included.

Asked about the relatively muted response to the loss of nearly 7,000 jobs when retailer Comet closed a couple of years ago - compared with the backlash to the possible loss of 15,000 Uk jobs at Tata Steel - he says it is partly because retail is "part of our everyday lives".

However, Mr Datson adds: "I wouldn't for a second suggest retail jobs are worth more than manufacturing jobs."  

BBC business correspondent Joe Lynam tweets:

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After tumbling on Friday, oil prices have continued to slide today as the chances of Middle East producers agreeing to end overproduction appeared to fade. 

Brent crude was down 1%, or 40 cents, at $38.27 a barrel in early trading, while US oil slipped 1.2%, to 43 cents, to $36.36.

Both indexes fell between 2% and 4% on Friday when Saudi Arabia said it would only participate in a global production freeze if Iran also took part - something Tehran has so far dismissed. 

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Independent pensions consultant John Ralfe tells Today it is “inevitable” that Tata Steel's pension fund, which dates back to the days of British Steel, will go into the Pension Protection Fund. The Tata scheme is worth about £15bn and has 130,000 members.

Although it is only has a deficit of between 3% and 5% - compared with an average of 20% - that is still a black hole of between £500m and £700m. The fund would be twice as big as the previous largest fund the PPF has had to take on, Mr Ralfe adds.

Joe Lynam is in the Today business presenter's chair on Monday