The Financial Services Authority (FSA) has confirmed it is investigating interest rate manipulation by other major high street banks after Barclays' record fine yesterday.
Barclays was hit with £290m in fines by financial regulators in the UK and the US after admitting its action "fell well short of standards", the BBC reports.
The FSA said its investigations into other banks were "ongoing" and from early signs Barclays was not the only bank involved.
The report said Barclays traders lied to make the bank look more secure during the financial crisis and sometimes, working with traders at other banks, to make a profit.
Tracey McDermott, director of enforcement at the FSA, which imposed fines alongside the US financial regulator, told the BBC: "We have a number of investigations that are ongoing.
"Obviously we need to look at each case on its own particular facts but the initial indications are that Barclays was not the only firm that was involved in this."
Other big names believed to be under investigation include Citigroup, JP Morgan, Deutsche Bank, HSBC and Royal Bank of Scotland, the report said.
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