The Serious Fraud Office (SFO) has made three arrests as part of its investigation into the manipulation of the interbank lending rate, Libor.
The major banks declined to comment on the development but Sky sources have suggested that one of the people detained used to work as a trader at the Swiss bank UBS (NYSEArca: DJCI - news) , which has a big presence in the City.
The SFO, with the assistance of the City of London Police, executed search warrants at three residential premises - one in Surrey and two in Essex.
It said in a statement: "Three men, aged 33, 41 and 47, have been arrested and taken to a London police station for interview in connection with the investigation into the manipulation of Libor."
It added: "The men are all British nationals currently living in the United Kingdom."
The SFO's criminal inquiry began in July when it decided existing legislation gave it the scope to bring potential prosecutions.
While the identities of those arrested and their employers are not known at this stage, it is known that the SFO's inquiry has been wide-ranging and not limited to Barclays (LSE: BARC.L - news) - the only UK bank so far to have been fined in connection with the scandal.
The £290m penalty inflicted on Barclays preceded the departure of its chief executive Bob Diamond and forced the British Bankers' Association to signal it would abandon its responsibility for oversight of Libor amid a clamour among politicians for reform.
Libor, which stands for London interbank offered rate, affects more than £350trn in global transactions and the rates created through the submissions bear a heavy influence in the calculation of a host of financial products including mortgages.
The City regulator, the Financial Services Authority (FSA), has been working closely with the SFO in its investigation.
A review of Libor by the FSA's boss Martin Wheatley has suggested a new body be created to oversee it with the rates set being based more on actual trades rather than just banks' own estimates.
Around 16 financial institutions have been investigated worldwide over alleged Libor rigging - including a total of three based in Britain.
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