A top Swiss banking official says that Germany would lose out if Berlin voted against a deal to end long-running tax evasion tensions with Switzerland.

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If the upper house of the German parliament on Friday votes down a deal on the taxation of German assets parked in Swiss bank accounts it would mean "lost money for the German state," the head of the Swiss Bankers' Association Claude-Alain Margelisch told reporters in Geneva on Wednesday.

Under the terms of the proposed tax deal between Bern and Berlin, Swiss banks would deduct taxes from German clients and transfer the tax revenues to Berlin — thus allowing the clients to remain anonymous.

German Finance Minister Wolfgang Schaeuble has estimated that the agreement could net his country around 10 billion euros ($12.8 billion) in tax payments.

Germany's lower house has already approved the deal but it is expected to have a bumpier ride on Friday when it comes before the upper house — the Bundesrat — where opponents believe the deal is too soft on tax-dodgers.

As long as the agreement was not signed, Margelisch said, "there would be a problem clearly for Germany," since it would miss out on the opportunity to lift a ten-year statute of limitation currently placed on its back-tax claims in Switzerland.

"If there is no deal signed, it's lost money for the German state," he said

If ratified, the tax deal is set to take effect on January 1st, and will entail taxation rates of between 21 and 41 percent on German assets held in Switzerland.

Switzerland has reached similar deals with Austria and Britain and is in discussions with Greece and Italy on the so-called "Rubik" accords.

Margelisch also stressed that a German green light for the deal could encourage other countries, like France, to agree to similar arrangements.

The banking chief said that the total managed assets in Swiss banks had risen again in the past year, indicating that investors were not frightened by the country's pending tax deals.

In total, banks in Switzerland managed assets worth nearly 5.3 trillion Swiss francs ($5.6 trillion) in 2011, Margelisch said,
pointing out that foreign assets continued to account for just over 50 percent of total assets under management.

"It would seem the expectation that foreign clients would withdraw huge sums if Swiss banks were to adopt a strategy of focusing on taxed assets and signing agreements with major partners is not being realised," he said.

As much as 180 billion euros ($231 billion) in undeclared German assets have been stashed in Switzerland, according to unconfirmed media reports.