London - British and US regulators are poised to levy hefty fines on leading banks in a landmark settlement after a year-long global investigation into allegations of collusion and manipulation in the foreign exchange market.
However, at least one of the six banks set to be named early on Wednesday morning by Britain's Financial Conduct Authority (FCA) remained in 11th-hour negotiations about details of the deal, two sources close to the matter said.
The banks at the centre of the UK investigation - UBS , Barclays , Royal Bank of Scotland, Citigroup, JPMorgan and HSBC - will also only sign off on an expected combined penalty of £1.5bn late on Tuesday, sources said.
READ: UK prepares forex fines for six banks -sources
It would be the first settlement over allegations of misconduct in the $5.3trn-a-day foreign exchange market. Around 35 traders have been suspended or fired by their banks after internal investigations, but no individual or institution has so far been charged with any wrongdoing.
However, the Wall Street Journal reported on Tuesday that Swiss financial regulator Finma had sent warning letters to around 10 past and present UBS employees about potential enforcement action for alleged misconduct in the forex market, according to sources familiar with the matter.
A spokesperson for Finma declined to comment. The FCA also declined comment.
As London accounts for around 40% of the market - double the size of nearest rival New York - the FCA has been keen to take a leading role in the global forex inquiry. Banks, meanwhile, have been keen to draw a line under the latest scandal weighing on their shares and tarnishing their reputations.
However, the Washington-based Commodity Futures Trading Commission (CFTC) and FINMA are also expected to be among those close to concluding investigations. Any US settlement is expected to name at least one other bank.
Bank of America said last week it was in "advanced discussions" with US bank regulators over foreign exchange matters.
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