Wealthy clients across Europe could withdraw "hundreds of billions of francs" from their Swiss banking accounts over the next few years as a direct result of international pressure targeting the nation's secretive banking practices, said UBS's Head of Wealth Management Juerg Zeltner on Monday.

In an interview with the Schweizer Bankmagazine, Zeltner predicted that his own company would see an outflow of at least 12-30 billion Swiss francs ($12.8-31.9 billion), though he emphasised how the company was making up for lost assets by attracting clients from emerging centres like Hong Kong, Singapore, Brazil, Mexico, Turkey and Russia.

"As a consequence of the realignment of the financial centre and the planned withholding tax, we assume that a total of hundreds of billions of francs will flow out of Switzerland," Zeltner said, as cited by Reuters.

"In the offshore business with European customers, I assume that we will have to live with significant outflows of wealth for quite a long time yet," he noted.

At present, the Swiss offshore banking sector is worth close to 2.7 trillion Swiss francs. But the industry has come under heavy fire in recent years as authorities from abroad hunt down wealthy citizens using secret Swiss accounts to evade taxes.

The U.S. for instance is investigating 11 Swiss banks on suspicion of helping US citizens dodge taxes; while Germany, Britain and Austria have each come to an agreement with Swiss authorities to tax their citizens' Swiss bank accounts.

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German financial services consultancy Zeb/Rolfes Schierenbeck Associates estimates that Swiss banks may see European clients pull up to 200 billion francs by 2016 of the 789 billion it believes they currently hold in untaxed assets.

Last week, Credit Suisse, Switzerland's second biggest bank, also forecasted that its clients in Western Europe may withdraw up to $37 billion in the next few years due to pressure on the tax issue.

Already, Zeltner claims, UBS has seen European clients take out around 10 billion francs from their accounts with the bank.

As the world's second largest private manager of wealth fund assets however, Zeltner believes that UBS still has plenty to offer to wealthy clients - even after Swiss banks lose their tax evasion appeal.

"There are legitimate reasons to have money outside your home, for example due to the high level of training in Switzerland or currency and political stability," he said.

"In particular in the area of very wealthy customers, there is strong demand for diversification of booking centres for assets. That will also be the case in the future," Zeltner added.

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According to AFP, many Swiss banks and wealth funds are also attempting to diversify their business in order to attract new clients.

"Banking secrecy is no longer there. That's gone. It is over," said international wealth management consultant Osmond Plummer during a gathering of Swiss bankers in Geneva last week.

"Something has to change in Switzerland," Plummer added, calling on Swiss banks to "concentrate on excellence" if they want to hold onto their current clients and attract new ones.