Italy and Switzerland on Monday signed a deal to recuperate billions of euros of taxes from wealthy Italians who stash their undeclared assets in the Alpine nation.

The plan includes a partial amnesty for account holders who now have until 30 September to pro-actively declare their Swiss accounts to the tax authorities. The "voluntary disclosure procedure" incurs fewer sanctions and drops most criminal charges.

Estimates suggest around 70 percent of Italian money hidden abroad is in Switzerland - a non-EU member - with the schemes reportedly costing Italy’s national coffers around €90 billion annually in lost revenue.

The signing comes in the wake of revelations known as Swissleaks in which account holders are being exposed. The Malta Independent has been in the forefront on this story, and last Sunday reported that former Nationalist Ministers Michael Falzon and Ninu Zammit had accounts in a Swiss bank.

"We have estimated additional revenues of just 1 euro in the budget law and the only thing I can say is that we will cash in more than that," Italy's economy minister Pier Carlo Padoan told reporters.

Bloomberg reports the undeclared Italian stash could amount to as much as €230 billion.

Swiss finance minister Eveline Widmer-Schlumpf said the deal would encourage account holders at Swiss banks "to come clean."

Switzerland is keen to improve its image on tax matters amid recent media reports that a Swiss branch of the UK banking giant HSBC was helping convicted criminals and other wealthy clients dupe tax authorities abroad.

The bank worked around a loophole in the 2003 EU-wide European savings directive (ESD) that requires authorities to impose a “withholding tax” on savings interest on offshore accounts.

Last week, Swiss prosecutors searched the offices of the Geneva-based subsidiary.