A Spanish court has on Tuesday rejected for a second time a Swiss extradition request for a former bank employee who is sought after having been given a five-year sentence for leaking data alleging widespread tax evasion by tens of thousands of account holders.

Former HSBC employee Herve Falciani was tried in Switzerland on charges of leaking banking details relating to some 120,000 accounts held in Swiss accounts and thus infringing the country's banking secrecy laws.

The National Court said in a statement that it had already rejected Falciani's extradition in a previous case following his 2012 arrest in Spain, arguing that the Swiss crime of aggravated financial espionage had no legal equivalent in the Spanish Penal Code.

It once again upheld its previous findings.

Falciani, 46, was born in Monaco and worked at HSBC's Swiss branch from 2001 to 2008 and was arrested following his arrival in Spain six years ago because of the existence of an official Swiss warrant.

Falciani, a computer analyst, began working for HSBC in 2000 before moving to bank's Geneva office in 2006, where he had access to secret, encrypted customer data.

He traveled to Lebanon in 2008 allegedly intending to sell the data, something that was condemned by Swiss authorities who were proud of their banking secrecy rules.

Later Falciani traveled to France, where he began collaborating with tax authorities, earning himself a reputation as a tax-evasion whistle-blower.