HSBC whistleblower warns that he has more information and could act again
Falciani previously said that 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 information technology worker at HSBC's Swiss subsidiary hinted in the interview published on Sunday that he could be moved to 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, 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 coordinated 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. They have so far said the information is confidential.
"It's only a question of political will to uncover that there is 10 times more than what we discovered at HSBC," Falciani is quoted as saying in the interview.
Falciani told El Mundo he had never worked alone in trying to uncover tax data at HSBC.
"From the beginning, I did everything with the help of others," he said. He added that there were several people within the bank who shared his views and that he had asked for help from contacts he had among police and customs specialists in Montecarlo.
Falciani did not specify what kind of help they had provided.
(Reporting by Sarah White; editing by Jane Baird)