Julian Assange, the WikiLeaks founder, today pledged to make public the confidential tax details of 2,000 wealthy and prominent individuals, after being passed the data by a Swiss banker who claims the information potentially reveals instances of money-laundering and large-scale illegal tax evasion.

In a carefully choreographed handover in central London, Rudolf Elmer, formerly a senior executive at the Swiss bank Julius Baer, based in the Cayman islands, said he was handing the data to WikiLeaks as part of an attempt "to educate society" about the amount of potential tax revenues lost thanks to offshore schemes and money-laundering.

"As banker, I have the right to stand up if something is wrong," he said. "I am against the system. I know how the system works and I know the day-to-day business. I want to let society know how this system works because it's damaging our society," he said.

Elmer will appear in a Swiss court on Wednesday charged with breaking Swiss banking secrecy laws, forging documents and sending threatening messages to two officials at his former employer.

He denies the charges.

He refused to comment on the period of time covered by the data, contained on two compact discs, or the precise source of the information; nor would he give the names of any corporations or individuals whose details he was handing over, saying that the information needed to be "investigated" before it was released into the public domain.

Assange, making his first public appearance since being bailed in December on sex assault allegations, for which Sweden is seeking his extradition, said he would pass the information to the Serious Fraud Office(SFO), examine it to ensure sources were protected, and then release it on the WikiLeaks site, potentially within "a couple of weeks".

"Once we look at the data, yes, there will be full disclosure," he said.

He would not be drawn on questions relating to the extradition case, which will be heard at Belmarsh magistrates court on 7 February, or on other leaks the site has promised are forthcoming, including information involving a "big US bank", which many believe to be Bank of America.

The site was not yet fully functional, he said. "We are not open yet for public business. The volume of material that we would receive is too high for our internal mechanisms, but we are receiving in other ways, like this, in this manner," he said. The release of leaked US diplomatic cables, which the site originally released through the Guardian and four other international media organisations, would continue, however. Elmer said he was passing the information to WikiLeaks because he had previously approached universities with the information but it had not been followed up. He said his attempts to interest the Swiss media had resulted only in his being dismissed as "a paranoid person, a mentally ill person".

"I was close to giving up, but then a friend of mine told me: 'There's WikiLeaks.' I looked at it and thought: 'That's the only hope I have to [let] society know what's going on.'"

In 2008, he released to the site a much smaller collection of documents, also detailing the tax details of some of the bank's clients. Though the site has never published that information, Julius Baer succeeded briefly in shutting down Wikileaks.org before the site, supported by a number of US media and civil liberties organisations, succeeded in overturning the injunction. He also passed the information to the US tax authorities.

The data was later seen by the Guardian, which found "details of numerous trusts in which wealthy people have placed capital. This allows them lawfully to avoid paying tax on profits, because legally it belongs to the trust"; the data also "[appeared] to include several cases where wealthy individuals sought to use trust money as though it were their own".

In a statement to the Observer on Friday, Julius Baer said: "The aim of [Elmer's] activities was, and is, to discredit Julius Baer as well as clients in the eyes of the public. With this goal in mind, Mr Elmer 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."

A spokeswoman for the SFO said it would "consider allegations made to it to determine if the matter is within its jurisdiction and criteria for investigation or possibly for another authority to consider".