Investigators will look into how French clients of HSBC could have opened accounts in Switzerland.

The probe will be based on a client list found by French authorities on the computer of a former employee of HSBC Private Bank, the largest foreign bank in Switzerland.

In 2009, French investigators seized the computer belonging to IT consultant Hervé Falciani, a 40-year-old French-Italian citizen, at the demand of Swiss authorities.

The data seizure listed 127,000 accounts belonging to 79,000 people including 8,231 French citizens.

The files, which were subsequently relayed by French investigators to their counterparts in the United States, Spain, Greece, Italy and several other European Union countries, led to a raft of prosecutions.

At the time, France opened an inquest targeting alleged tax evaders on the list, but the probe proved fruitless, pushing magistrates to attempt this latest investigation targeting illegal activity by HSBC itself.

The inquest is implicitly looking to uncover illegal efforts by the banking giant to drum up business in France for its branch in Switzerland.

Falciani is currently fighting an extradition to Switzerland, where he is wanted for breaking the country's highly cherished banking secrecy laws.