ZURICH, Dec 22 (Reuters) - A Swiss court has allowed the extradition to Germany of Hanno Berger, a German lawyer and tax specialist accused of playing a key role in a years-long tax fraud. The scandal, known as "cum-ex", is Germany"s biggest post-war fraud involving a share-trading scheme that the authorities say cost taxpayers billions of euros. According to prosecutors, the scheme was promoted by Berger, a German tax inspector-turned-tax adviser, and others. Berger, 71, who helped represent himself, has always denied any wrongdoing and said what he did was within the law. His Swiss attorney was not immediately available for comment on the ruling by the Federal Criminal Court, which can be appealed to Switzerland"s supreme court. Berger was arrested in the Swiss canton of Grisons on July 7 based on an extradition request from Germany. read more The scheme involved trading stocks of major companies rapidly around a syndicate of banks, investors and hedge funds to give the impression of numerous owners, each entitled to a bogus tax rebate. The practice thrived between 2005 and 2012, a period that included the years after a financial crash and as banks were bailed out by the state. A loophole that fostered the trades was then closed. The cum-ex tax fraud is the subject of multiple investigations across Germany as the government tries to claw back billions in euros it said were stolen from the state.