Tullett Prebon, one of the world's biggest inter-dealer money brokers, saw its share price tumble after a report in the Financial Times alleged that one of the firm's staff is implicated in the Libor fixing scandal.
Citing anonymous sources close to the Financial Services Authority's (FSA) probe into attempted rate-manipulation by some of Britain's biggest banks, the FT reported that one of the unnamed brokers listed in the investigations that found RBS and UBS guilty of trying to fix Libor worked for Tullett.
Tullett said that neither the FSA nor any other global regulator had informed them that it or any of its brokers had been under investigation in connection with Libor manipulation.
Shares in Tullett were down over 6 percent at midday on the London Stock Exchange.
RBS, which is 83 percent owned by the taxpayer after a financial crisis bailout, agreed to an £87.5m fine from the FSA after the regulator found evidence its staff had tried to fix Libor for US dollar, Japanese yen, and Swiss franc submissions.
Swiss investment bank UBS agreed to a £160m with the FSA for its role in attempts to manipulate Libor.
The FSA said it found at least 2,000 documents showing attempts to manipulate the benchmark interbank lending rate, which underpins around $500tn worth of global financial securities.
Smoking-gun emails have been published by the FSA as it revealed the results of its investigations.
"If you keep 6s unchanged today ... I will f***ing do one humongous deal with you ... Like a 50,000 buck deal, whatever ... I need you to keep it as low as possible ... if you do that .... I'll pay you, you know, 50,000 dollars, 100,000 dollars... whatever you want ... I'm a man of my word," read one example from 18 September 2008, where a trader attempted to convince a broker to lower his rate submission for six-month libor denominated in Yen.