A former Swiss private banker Rudolf Elmer has handed over data on two thousand of offshore bank account holders to the WikiLeaks website founder Julian Assange at a London news conference on Monday.

Elmer is a former director the office of Julius Baer bank in the Cayman Islands until he was fired by the bank in 2002. He is scheduled to go on trial in Switzerland on Wednesday for breaching bank secrecy.

He handed over the data at the press conference in a media center in London, Reuters reported.

"He (Elmer) is clearly a bona fide whistleblower... We have some kind of duty to support him in that matter," said Assange, who is on bail in Britain and fighting extradition to Sweden where he faces questioning over alleged sex crimes.

Elmer, who worked in the Cayman Islands for eight years, said: "I know how the system works... It's damaging... (I want) to educate our society."

WikiLeaks will examine the data before publishing it. Examining will be done by themselves, media organisations and other partners to protect sources amongst other concerns. Assange said the process will take at least two weeks, Reuters reported.

Elmer told Reuters that he hoped he would both call attention to offshore financial abuses and promote WikiLeaks as a mechanism for other whistleblowers to air their stories.

However, Julius Baer said Elmer had other motives.

"After his demands (including financial compensation) in connection with the dismissal could not be satisfied, Mr Elmer embarked in 2004 on a personal intimidation campaign and vendetta against Julius Baer," the bank said in a statement.

"The aim of his activities was and is to discredit Julius Baer as well as clients in the eyes of the public."