RBS is fighting the Treasury in court over six-figure bonuses of a group of metal traders paid into an offshore trust, according to sources.
Bonuses from a number of employees of RBS Sempra Metals now owned by the part-nationalised bank were paid into an offshore trust in a bid to dodge income tax and national insurance contributions, reports The Guardian.
Cash was provided to the traders' spouses as 'loans' amounting to nearly £1m in some cases and was often used to pay mortgages and purchase property.
A tax tribunal last year found the group had a history of trying to avoid tax and national insurance contributions with schemes including taking payments in precious metals and making loans that went unpaid.
The tribunal found cash shared between 30 senior employees could double a trader's salary, "but in a good year could amount to a significant multiple of his annual salary".
RBS bought control of Sempra Metals in April 2008 before the bail-out and says bonus payments into the Isle of Man were curtailed when it took over.
However a high court ruling has continued and is due to be heard in March.
The tribunal ruled Sempra should pay 30% corporation tax on the bonus fund but did not rule individual employees are liable for their share.
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