The offshore bank account details of 2,000 "high net worth individuals" and corporations - detailing massive potential tax evasion - will be handed over to the WikiLeaks organisation in London tomorrow by the most important and boldest whistleblower in Swiss banking history, Rudolf Elmer, two days before he goes on trial in his native Switzerland.

British and American individuals and companies are among the offshore clients whose details will be contained on CDs presented to WikiLeaks at the Frontline Club in London. Those involved include, Elmer tells the Observer, "approximately 40 politicians".

Elmer, who after his press conference will return to Switzerland from exile in Mauritius to face trial, is a former chief operating officer in the Cayman Islands and employee of the powerful Julius Baer bank, which accuses him of stealing the information.

He is also - at a time when the activities of banks are a matter of public concern - one of a small band of employees and executives seeking to blow the whistle on what they see as unprofessional, immoral and even potentially criminal activity by powerful international financial institutions.

Along with the City of London and Wall Street, Switzerland is a fortress of banking and financial services, but famously secretive and expert in the concealment of wealth from all over the world for tax evasion and other extra-legal purposes.

Elmer says he is releasing the information "in order to educate society". The list includes "high net worth individuals", multinational conglomerates and financial institutions - hedge funds". They are said to be "using secrecy as a screen to hide behind in order to avoid paying tax". They come from the US, Britain, Germany, Austria and Asia - "from all over".

Clients include "business people, politicians, people who have made their living in the arts and multinational conglomerates - from both sides of the Atlantic". Elmer says: "Well-known pillars of society will hold investment portfolios and may include houses, trading companies, artwork, yachts, jewellery, horses, and so on."

"What I am objecting to is not one particular bank, but a system of structures," he told the Observer. "I have worked for major banks other than Julius Baer, and the one thing on which I am absolutely clear is that the banks know, and the big boys know, that money is being secreted away for tax-evasion purposes, and other things such as money-laundering - although these cases involve tax evasion."

Swiss Whistleblower Rudolf Elmer plans to hand over offshore banking secrets of the rich & famous to Wikileaks