Rudolf Elmer presented CDs containing the information, which he claims reveals potential tax evasion, to WikiLeaks at the Frontline Club in London this morning, two days before he goes on trial in Switzerland.

The former Julius Baer COO in the Cayman Islands earlier told the Observer that he is handing over the data on multinationals, hedge funds, artists and around 40 politicians, which comes from three financial institutions, "in order to educate society".

WikiLeaks founder Julian Assange, currently on bail, was at the press conference to receive the data, which he said would be vetted before publication, with some potentially handed over the Serious Fraud Office.

At the conference, Assange also told reporters that in 2008 Julius Baer went to court in the US in a failed bid to have WikiLeaks.org shut down over previous revelations.

In fact, he says "we have had more legal threats and attempted lawsuits by banks than any other organisations. None have been successful and I do not expect them to be successful in the future."

Assange also hit out at credit card companies over their refusal to process payments for WikiLeaks, saying they "operate outside the rule of law" and are "entirely responsive to political influence". WikiLeaks has been "economically censored" by Visa, MasterCard, Mooneybookers, Bank of America, PayPal, Amazon and Western Europe, he argued.

He says the organisation is involved in "preliminary action" against Visa Europe.

Since leaving Julius Baer in 2004, Elmer has become a self-styled whistleblower seeking to expose the use of offshore accounts for tax evasion, describing himself on his Website, swisswhistleblower.com, as an activist, reformer and banker.

On Wednesday the ex-banker faces trial in Switzerland over allegations that he breached bank secrecy and threatened Julius Baer officials.

The bank told the Observer that its ex-employee has "spread baseless accusations and passed on unlawfully acquired, respectively retained, documents to the media, and later also to WikiLeaks. To back up his campaign, he also used falsified documents".