Fincen files: How British companies use banks to money launder

The FinCEN Files consist of more than 2,500 documents which were sent to US financial authorities reporting banks' concerns about their clients.

FinCEN is the US Financial Crimes Investigation Network.

Concerns about transactions made in US dollars need to be sent to FinCEN, even if they took place outside the US.

Suspicious activity reports, or SARs, are an example of how those concerns are recorded. A bank must fill in one of these reports if it is worried one of its clients might be up to no good. The report is sent to the authorities.

The files were obtained by BuzzFeed News which shared them with the International Consortium of Investigative Journalists (ICIJ) and 400 journalists around the world. Panorama has led research for the BBC.