Frank Serpico - New York police officer who exposed corruption in NYPD

Daniel Ellsberg - leaked Pentagon Papers to New York Times

Francis 'Chalkie' White - confronted paedophile George Gibney

Harry Templeton - stood up to publish Robert Maxwell

Colin Wallace - British Army dirty tricks in 1970s

David Kaczynski - brother of the Unabomber

Tom Clonan - Irish Army whistleblower

By 2000, the Enron Corporation was a colossus. It was America's seventh largest company, employed 27,000 staff, and was a multi-billion dollar operation. Its management were close friends of both Bush presidents, and were making - in some cases - hundreds of millions of dollars each. A year later, in the fall out that followed the Enron implosion, it emerged that - months before the scandal broke - one voice inside Enron had been trying to alert management to the looming accounting scandal.

In 1971, Daniel Ellsberg made history by releasing to the New York Times top-secret Government documents which became known as the 'Pentagon Papers'. The leak set in motion a chain of events that ended the Nixon presidency and the Vietnam War.

Mukesh Kapila was head of the UN in Sudan in 2004 when he blew the whistle on the crisis in Darfur, and the UN’s failure to respond to it.