Swiss whistleblower Rudolf Elmer is planning to handover to WikiLeaks two CDs containing data of around 2,000 bank clients who may have been evading taxes, according to an interview published Sunday.

"The documents show that they are hiding behind bank secrecy, possibly to avoid taxes," Elmer, a former Swiss banker, told Swiss newspaper Sonntag.

The data is to be handed over on Monday, during a press conference in London.

The event will take place at the Frontline Club -- a media club where WikiLeaks operates in Britain -- from 11:15 am (1115 GMT).

Elmer "will reveal more details of alleged abuses in the world of offshore financial centres," the Club said on its website.

"As he did back in 2007 he will pass the said documents and information to WikiLeaks. A representative from WikiLeaks will be attending to accept this information," it added.

Sonntag said that WikiLeaks founder Julian Assange would also be present at the press conference. However his lawyer would not confirm the report and Assange's appearance would turn out to be a surprise given the terms of his bail.

The Australian is on bail in Britain awaiting Sweden's attempt to extradite him for questioning on sexual assault allegations.

A full extradition hearing will be heard at a London court on February 7-8.

Assange's bail conditions for the hearing have meanwhile been altered, allowing him to stay at the Frontline Club on the nights of February 6 and February 7.

According to Sonntag, the information set to be disclosed by Elmer on Monday will not be published immediately on the whistleblower website.

"WikiLeaks will go through the data, and if they really deal with tax evasion, they will be published later."

According to Elmer, the clients listed on the two discs include multimillionaires, multinationals and hedge funds from several countries, including Switzerland, the United States, Germany and Britain.

The data also implicate around 40 politicians.

Elmer said that the data stems from at least three financial institutions and cover the period of 1990 and 2009.

Elmer, who was a director at Bank Julius Baer in Cayman Islands, is meanwhile to appear before a Zurich court on Wednesday to answer to charges of bank secrecy violations, after he passed on clients' data to WikiLeaks in 2007.

The move led to tax evasion prosecutions in several countries against these clients.