Mr Falciani previously said media leaks on HSBC accounts held in Switzerland, which unleashed a public storm around the British bank, were “only the tip of the iceberg”, and that tax authorities had access to a lot more data.
The former IT worker at HSBC’s Swiss subsidiary hinted in the interview yesterday that he could make more revelations.
“My work is still not done. We’re not in a hurry. It’s possible that at the end of the year, we’ll have the opportunity to act”, he said after being asked by El Mundo whether he would lift the lid on further tax cases if Spanish authorities did not.
Several high-profile Spaniards have been affected by the Falciani leaks.
The International Consortium of Investigative Journalists, which in February co-ordinated the media release of details of leaked client data, said account-holders included ex-Santander chairman Emilio Botin, who died last year.
Spanish authorities are also coming under pressure from opposition parties to reveal which public figures feature on a list of people who signed up to a recent tax amnesty, especially as a general election nears.
“It’s only a question of political will to uncover that there is 10 times more than what we discovered at HSBC,” said Mr Falciani.