* Germany probes sham trades, double tax reclaims
* British banker plays down his role in scheme
* Trial could pave way for Germany to pursue others
By John O'Donnell
BONN, Sept 25 (Reuters) - A British banker told Germany's biggest fraud trial this week how he worked his way from office clerk to jet-setting trader before his dream career came to an early end.
Nicholas Diable, 38, is one of two British bankers who German prosecutors allege orchestrated a sham trading scheme to make illegitimate double tax reclaims of more than 450 million euros ($495 million).
Diable, who has not denied he was involved in the 'cum-ex' trading but says he had no reason to believe it was illegal, played down his role during the court hearing in Bonn.
He described his work as that of a salaried technician with a focus on getting trades done rather than a mastermind.
"For me, it was only a question of whether the trade was possible or not," Diable told the German judges on Wednesday.
State prosecutor Anne Brorhilker this month outlined criminal charges against Diable and Martin Shields, who both face a possible jail term as well as a court order to repay money they earned from the trades if found guilty.
Diable answered the accusation at his trial, the first criminal case brought against those involved in 'cum-ex' trading, a practice described by German finance minister Olaf Scholz as a "scandal".
Prosecutors allege that players in the scheme misled the state into thinking a stock had multiple owners who were each owed a dividend and a tax credit. Germany estimates such trades cost it more than 5 billion euros in total.
If successful, this case would make it easier to pursue others and recover the money lost.
Brorhilker said the two men had targeted companies including carmaker BMW and airline Lufthansa, outlining more than 30 instances of double-tax reclaims totalling 447 million euros.
Shields told the court last week that he regretted his involvement in the "industrial scale" trading scheme, but that the practice was common knowledge and that he had no reason to believe at the time that it was legally questionable.
The 41-year-old Oxford university graduate said the trading thrived between 2005 and 2012, as investors from around the globe made multi-billion-euro trades on German companies.
Diable emphasised his more technical, junior role, telling judges about his modest start in the City of London, inputting data, taking lunch orders and rituals such as running through an office as colleagues threw objects at him.
He later became a trader and worked with Shields at German bank HVB, carrying out such trades, before following him to Gibraltar, when Shields set up his own company.
Both jobs involved entertaining customers and contacts in "bars and restaurants" in London, at Germany's Oktoberfest beer festival, as well as in Gibraltar, Diable said.
Diable said he had been under investigation since he was 31 during a statement made to the court over two days outlining the mechanics of the trading.
The alleged scheme involved trading shares rapidly around a syndicate of banks, investors and hedge funds to give the impression of numerous owners, each entitled to a tax rebate.
The case, Germany's biggest post-war fraud investigation, is being closely followed in London and Frankfurt, where much of the trading was organised, according to bankers and court documents.
HVB, which has blamed its involvement on wrongdoing by individuals, has declined further comment. ($1 = 0.9100 euros) (Reporting by John O'Donnell; Editing by Alexander Smith)