The Pandora Papers is a leak of almost 12 million documents that reveal hidden wealth, tax avoidance and, in some cases, money laundering by some of the world's rich and powerful.

More than 600 journalists in 117 countries have been trawling through the files from 14 sources for months, finding stories that are being published this week.

The data was obtained by the International Consortium of Investigative Journalists (ICIJ) in Washington DC, which has been working with more than 140 media organisations on its biggest ever global investigation.

BBC Panorama and the Guardian have led the investigation in the UK.

The Pandora Papers leak includes 6.4 million documents, almost three million images, more than a million emails and almost half a million spreadsheets.

Stories revealed so far include:

The Pandora Papers reveal complex networks of companies that are set up across borders, often resulting in hidden ownership of money and assets.

For example, someone may have a property in the UK, but own it via a chain of companies based in other countries, or "offshore".

These offshore countries or territories are where:

The destinations are often called tax havens or secrecy jurisdictions. There is no definitive list of tax havens, but the most well-known destinations include British Overseas Territories such as the Cayman Islands and the British Virgin Islands, as well as countries such as Switzerland and Singapore.

Loopholes in the law allow people to legally avoid paying some taxes by moving their money or setting up companies in tax havens, but it is often seen as unethical. The UK government says tax avoidance "involves operating within the letter, but not the spirit, of the law".

There are also a number of legitimate reasons people may want to hold money and assets in different countries, such as protection from criminal attacks or guarding against unstable governments.

Although having secretive offshore assets is not illegal, using a complex network of secret companies to move around money and assets is the perfect way to hide the proceeds of criminality.

There have been repeated calls for politicians to make it harder to avoid tax or hide assets, particularly following previous leaks such as the Panama Papers.

But Mr Ryle said the Pandora Papers show that "the people that could end the secrecy offshore… are themselves benefiting from it. So there's no incentive for them to end it". 

All you need to do is set up a shell company in one of the countries or jurisdictions with high levels of secrecy. This is a company that exists in name only, with no staff or office.

It costs money though. Specialist firms are paid to set up and run shell companies on your behalf. These firms can provide an address and names of paid directors, therefore leaving no trail of who is ultimately behind the business.