The Financial Conduct Authority is looking into the WM/Reuters benchmark, the latest to be studied in a series of probes covering indices including Libor.
The RBS trader in question left his job at the bank for unrelated reasons, according to Bloomberg News.
RBS was fined £390m last year after regulators found some of its traders had conspired to manipulate key interbank interest rates. RBS and the FCA declined to comment.
Meanwhile RBS won the final stage of a court case against a business customer who claimed the bank mis-sold it an interest rate swap.
The Lancashire hoteliers were deemed sophisticated customers, and so could not use the FCA’s redress scheme, instead taking the bank to court. But its claim was rejected, and it yesterday lost the right to appeal.
The case was considered a typical swap, and so may reduce the chance of similar cases being brought against the bank.